the crustacea

Transcription

the crustacea

T REATISE ON Z OOLOGY – A NATOMY, TAXONOMY, B IOLOGY
THE CRUSTACEA
R EVISED AND UPDATED , AS WELL AS EXTENDED FROM THE
TRAITÉ DE ZOOLOGIE
[Founded by P.-P. GRASSÉ (†)]
Edited by
J. C. von VAUPEL KLEIN, M. CHARMANTIER-DAURES
and F. R. SCHRAM
VOLUME 4
PART B
With contributions by
A. P. Ariani, H.-M. Cauchie, G. Charmantier, J.-P. Lagardère, L. Laubier (†),
Th. Monod (†), P. Noël, K. J. Wittmann
English translations by
J. C. von Vaupel Klein and F. R. Schram
BRILL
LEIDEN · BOSTON
2014
© 2014 Koninklijke Brill NV ISBN 978 90 04 26492 2
CONTENTS
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
P IERRE N OËL , T HÉODORE M ONOD (†) & L UCIEN L AUBIER (†), Crustacea in
the biosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
H ENRY-M ICHEL C AUCHIE , T HÉODORE M ONOD (†) & L UCIEN L AUBIER (†),
Crustaceans and mankind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
G UY C HARMANTIER, Crustaceans in art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
K ARL J. W ITTMANN , A NTONIO P. A RIANI & J EAN -PAUL L AGARDÈRE, Orders
Lophogastrida Boas, 1883, Stygiomysida Tchindonova, 1981, and Mysida Boas,
1883 (also known collectively as Mysidacea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Colour figures of vol. 4B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
List of contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Taxonomic index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Subject index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Errata TOZ-C vol. 4A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3
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CHAPTER 54
ORDERS LOPHOGASTRIDA BOAS, 1883,
STYGIOMYSIDA TCHINDONOVA, 1981,
AND MYSIDA BOAS, 1883
(ALSO KNOWN COLLECTIVELY AS MYSIDACEA)1 )
BY
KARL J. WITTMANN, ANTONIO P. ARIANI AND JEAN-PAUL LAGARDÈRE
Contents. – Introduction – Outline of the orders – Historical outline – Terminology and definitions.
External morphology – Habitus – Size of adults – Carapace – Cephalothorax – Pleon – Telson
– Integument and colour – Cephalic appendages – Thoracic appendages – Pleonal appendages.
Internal morphology – Musculature – Nervous system – Sensory organs – Digestive system
and digestion – Circulatory system – Respiratory system – Reproductive system – Excretory
system and excretion – Endocrine organs. Reproduction and sexuality – Sexual dimorphism
– Intersexuality – Sex ratio – Mating and oviposition – Fecundity – Incubation – Adjustment
of reproductive parameters. Development and moulting – Marsupial development – Moulting
and growth – Regeneration – Life cycle. Ecology and ethology – Habitat and distribution –
Locomotion, orientation, and taxis – Migration – Social aggregation – Grooming – Food and feeding
– Trophic interactions – Symbiotic associations – Parasites. Ecological and economic importance
– Contribution to biodiversity – Impact on ecosystems – Importance in fisheries. Phylogeny
and biogeography – Fossil record – Phylogeny – Biogeography. Systematics – Guidelines to
classification – Classification – Keys to the families, subfamilies, and tribes of the Lophogastrida,
Stygiomysida, and Mysida. Appendix. Acknowledgements. Bibliography.
INTRODUCTION
The unity or disunity of the Mysidacea as competing hypotheses is currently among
the central controversies in phylogenetic research on malacostracan Crustacea. In the first
1 ) Revised and updated from the treatise by H. Nouvel (†), J.-P. Casanova & J.-P. Lagardère (1999),
November 2013; latest additions February 2014.
© Koninklijke Brill NV, Leiden, 2014
4B (54): 189-396
© 2014 Koninklijke Brill NV ISBN 978 90Crustacea
04 26492
2
190
K. J. WITTMANN, A. P. ARIANI & J.-P. LAGARDÈRE
volume of the present series, Forest (2004) noted that the traditional systematics, which
outline the unity of the order Mysidacea as a container for the suborders Mysida and
Lophogastrida, is under discussion. As an alternative hypothesis he noted a potential placement of the Mysida outside the Peracarida, in this case he envisaged a potential approach
to the Eucarida. Ultimately, however he inclined towards the traditional hypothesis and
scheduled the Mysidacea to be treated at order level in the present series. Meanwhile,
new morphological evidence (Wirkner & Richter, 2007, 2010) would seem to favour
the traditional hypothesis, whereas new genetic evidence (Spears et al., 2005; Meland &
Willassen, 2007) points to the alternative hypothesis. Jenner et al. (2009), in turn, argued
that any previously published evidence is unable to solve the problem. In fact, both competing hypotheses are strongly supported by data, and no definite decisions can yet be seen
to emerge. As a provisional option within a controversial environment, the Lophogastrida,
Stygiomysida, and Mysida are treated here as separate orders, as discussed below in ‘Outline of history’ and ‘Phylogeny’.
Outline of the orders
The Lophogastrida, Stygiomysida, and Mysida have a great number of characters in
common, stimulating decade-long discussions on the extent to which these characters are
plesiomorphic within the Malacostraca and whether these taxa are to be kept separately
or to be united in the traditional order Mysidacea (see below, ‘Outline of history’ and
‘Phylogeny’). Together they represent shrimp-like (figs. 54.1-54.5) Eumalacostraca, at
least some of them pertaining to the Peracarida. The well-developed carapace covers
most of the cephalothorax, or even the entire cephalothorax in certain Lophogastrida
(Gnathophausia, Chalaraspidum; fig. 54.2A, C). It is fused dorsally with the cephalic
region and at most four anterior thoracic somites, and projects freely above some of
the posterior ones (exceptions below, ‘Carapace’). The free space below the carapace
contributes to a carapace cavity. Dorsally, the carapace is often divided by a distinct,
transverse cervical sulcus (figs. 54.4, 54.5, 54.7E, F, 54.9G), in lateral view located more
or less above the mandibles. Laterally it is mostly not fused with the thoracic pleurites,
leaving space for the lateral portions of the carapace cavity. Respiratory tissue is provided
by the wall of the carapace cavity (fig. 54.31D; Mysida and Stygiomysida) or by gills
on the coxae of the thoracic appendages (figs. 54.6E, 54.16C, E, G; Lophogastrida). The
respiratory current is to a minor extent driven by a small leaf-like, first thoracic epipod,
but mainly by the movements of the thoracic exopods. Paired compound eyes are normally
well developed, moveable by eyestalks. Stalks and/or cornea are occasionally fused and/or
reduced, particularly in species from deep-water and subterranean habitats. Eight pairs
of thoracopods are present (figs. 54.16, 54.17), their exopods with a basal plate and
with a setose multi-segmented flagellum. The exopods serve for swimming and support
respiratory currents, in many species also filtration currents. Exopods 1, 2, and 8 may
be reduced or absent in certain taxa (figs. 54.16A, B, 54.17A, B). The anterior 1-2, in
certain taxa up to 3-4, pairs of thoracic endopods are mostly specialized as maxillipeds
(figs. 54.15M, N, 54.16A-C, 54.17A-C) or ‘gnathopods’ (fig. 54.18H). The remaining
ORDERS LOPHOGASTRIDA, STYGIOMYSIDA, AND MYSIDA
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endopods were previously often termed ‘pereiopods’ (e.g., Tattersall & Tattersall, 1951)
but are equipped for manipulations such as grasping food rather than for walking, although
some crawling does occur. As in most Eumalacostraca, the gonopores are located on
the coxae of the sixth thoracopods in females, and of the eighth thoracopods in males
(fig. 54.20). The uropods are well developed, biramous, and flattened. Together with
the telson they form a strong tail fan (fig. 54.22) suitable to support body flipping for
sudden escape movements. The brood pouch or marsupium (fig. 54.19) is formed by
1-7 pairs of oostegites on the posterior thoracic appendages. The young pass through an
embryonic and two non-feeding larval stages within the marsupium. They are liberated
as miniature ‘adults’ equipped with all appendages and capable of self-sustained life, but
lacking secondary sexual characteristics.
The Lophogastrida (figs. 54.1A, 54.2) are characterized by external gills (fig. 54.6E,
G), seven pairs of oostegites (fig. 54.19A), and well developed pleopods (natatory in both
sexes). With the Stygiomysida (figs. 54.1B, C, 54.3) they share the absence of statocysts
in the tail fan and the absence of well-developed tubular penes. The Stygiomysida have
4-7 pairs of oostegites (fig. 54.19D), bilobate male gonopores (fig. 54.20B; Wittmann,
2013b), biramous pleopods (fig. 54.17G-K) with largely, but never entirely, reduced rami
in both sexes, and spinose inner lobes on the sympods of the uropods (fig. 54.22F-H).
They share the absence of gills with the Mysida (figs. 54.1D, E, 54.4, 54.5). This order
is characterized by 1-7 pairs (mostly 2-3) of functional oostegites, in most taxa also by
the presence of statocysts in the endopods of the uropods (figs. 54.22K-O, 54.26, 54.27),
and well-developed tubular penes (fig. 54.20C, E-G); with few exceptions the pleopods are
reduced to small, unsegmented rods or plates in females (fig. 54.21F, H), in part also in
males (fig. 54.21R-U).
Historical outline
An excellent overview of the classification history of Crustacea is given in the third
volume of the present series (Monod & Forest, 2012), mainly dealing with class to order
levels. The present outline gives complementary information about the difficult birth, the
rise, and the potential decline or renaissance of the order Mysidacea Boas, 1883.
The first mysid taxa. – The first description of a species of the Mysida in today’s understanding was given by O. F. Müller (1776) for Cancer flexuosus, defined as “Macrourus
pedibus pectoris duplici serie, abdominis membranis, quinque utrinque, branchialibus”.
Today it is known as Praunus flexuosus, a common near-shore species from coastal waters
of the north-east Atlantic and the Baltic. Shortly thereafter, Slabber (1778) published the
first realistic drawing of a mysid species, based on the knowledge of that time correctly
identified by him as Cancer, today known as Mesopodopsis slabberi. A few years later,
Fabricius (1780) established a number of new taxa — Cancer pedatus, Cancer bipes, and
Cancer oculatus — from waters off Greenland. All his types have been lost. These taxa
experienced quite different fates: Cancer pedatus remained of obscure identity (according
to Holmquist, 1958, possibly any euphausiacean), Cancer bipes became the well-known
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Fig. 54.1. Diversity of Lophogastrida (A), Stygiomysida (B, C), and Mysida (D, E). A, Gnathophausia zoea Willemoës-Suhm, 1873; B, Stygiomysis hydruntina Caroli, 1937; C, Spelaeomysis bottazzii
Caroli, 1924; D, Heteromysis wirtzi Wittmann, 2008; E, Hemimysis lamornae mediterranea Băcescu,
1937. [A, photo José Antonio González; B, after Inguscio, 1998; C, E, photo Antonio P. Ariani; D,
after Wittmann, 2008 (photo Peter Wirtz).]
leptostracan Nebalia bipes, and Cancer oculatus became the now well-known mysid Mysis
oculata, widely distributed in Arctic waters.
Establishment of Mysis. – Explicitly referring to Cancer pedatus, Latreille (1802)
established the genus Mysis, and associated Cancer oculatus and Cancer bipes with his
new genus. The etymology of ‘Mysis’ was not indicated, so it remained unclear which, if
any, of several potential meanings was intended by him. No later authors commented on the
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fact that Agassiz (1843: 19) and similarly also Costa (1847: 3, in footnote) had indicated
for the genus Mysis “μύσις, oculorum conniventia” (transl.: “mysis, closing of eyes”),
obviously referring to the Greek noun μύσις (musis = mýsis = the pressing together of
lips or eyelids; Hentschel & Wagner, 1976). Nonetheless, the meaning is obscure in the
present context and these etymological notes appear to simply be literal translations.
Inversion of Mysis. – Leach (1815) redefined the morphological concept of the genus
Mysis by adding just the brood pouch — not mentioned by previous authors — as a diagnostic character: “Ad feminae abdominis basin est uterus externus e membranis duobus
concavis falvuliformibus eformatus, quo pulli nuper ex ovo exclusi vivunt, crescunt”. He
restricted Mysis to three species rearranged by him, one of which, Mysis Fabricii, is today
considered a junior synonym of Mysis oculata. From that time onwards most authors emphasized Mysis as a mysid in today’s understanding. In 1830, Leach described a new genus
and species, Megalophthalmus Fabricianus, and referred Cancer pedatus to the new taxon.
In conclusion, by his combined papers from 1815 and 1830, he had inverted the precedence
explicitly indicated by Latreille (1802) for Cancer pedatus over Cancer oculatus as type
species of the genus Mysis. No types are known for Megalophthalmus Fabricianus, which
remained essentially unrecognizable; nonetheless, it was tentatively referred to different
Mysis species by various authors (Holmquist, 1958).
Further establishment and crisis. – The redefined Mysis became type genus of the
family Mysidae Haworth, 1825, and later also of the suborder Mysida Boas, 1883, the
order Mysidacea Boas, 1883, and also of additional, today poorly known and outdated
higher taxa, such as the suborder (as “Tribus”) Mysidea Dana, 1852, and the superorder
Mysiformida Czerniavsky, 1882. Despite being originally based on a taxon of obscure
identity, the Mysis-based taxa and terminologies proposed by various authors (Haworth,
1825; Burmeister, 1837; Dana, 1852; Czerniavsky, 1882; Boas, 1883; Norman, 1892; Calman, 1904; Hansen, 1910) remained collectively stable for many decades. They then came
under risk of collapsing due to the priority rules explicitly established with the nomenclatural code in the 20th century. Tattersall & Tattersall (1951) tried to circumvent the
problem by claiming that “C. pedatus has not been identified with certainty, but is probably a synonym of C. oculatus”. However, their attempted solution is poorly compatible
with the species descriptions given by Fabricius (1780) and, in addition would have required a reversal of precedence. Holmquist (1958) proposed as an effective solution that
the International Commission on Zoological Nomenclature (ICZN) should use its plenary
power to suppress the taxon Cancer pedatus Fabricius, 1780, and to fix Cancer oculatus
Fabricius, 1780, as the type species of Mysis. Finally, these proposals were adopted by the
ICZN (1959) together with a package of additional rules necessary in this context.
Schizopoda. – In 1817, Latreille established the Schizopodes (later termed Schizopoda)
for reception of mysids and leptostracans, characterized by a well-developed carapace
and biramous thoracopods. This system was developed further by Latreille (1825), H.
Milne Edwards (1837), Dana (1852), and others. Then including the Euphausiacea, the
Schizopoda became a widely acknowledged standard for many decades in various variants,
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including (Czerniavsky, 1882) or excluding (G. O. Sars, 1885a; Zimmer, 1909; Illig, 1930)
the leptostracans.
Lophogastrida. – The age of the great oceanographic expeditions yielded the first
lophogastrids. Almost eight decades after the first description of a mysid, the first
lophogastrid was described by Dana (1852) as Eucopia australis. Based on this species,
he established the Eucopidae (now Eucopiidae) as a new family within penaeid decapods
by defining “Carapax non rostratus, fronte integro. Pedes thoracici elongato-palpigeri,
palpis natatoriis. Maxillipedes 2di 3tii et pedes 1mi monodactyli et suprehensiles”.
A few years later, M. Sars (1857) established the genus Lophogaster with the species
Lophogaster typicus, a benthopelagic crustacean with wide distribution in the eastern
Atlantic and Mediterranean. The generic name is derived from the Greek λóϕoς (= tuft,
mane) and γαστήρ (= stomach). In 1870, his son G. O. Sars used this genus to
define the family Lophogastridae within the Schizopoda. Based on considerations on the
homology of crustacean appendages, Boas (1883) aborted the Schizopoda and placed the
Lophogastridae (without Eucopiidae) together with the Mysidae, both distant from the
Euphausiacea, at suborder rank within the order Mysidacea, established by him. In fact,
Lophogastrida and Mysida share a great number of morphological characters, as shown
above in ‘Outline of the orders’.
Stygiomysida. – The first representative of this order, Spelaeomysis bottazzii, was discovered in subterranean waters of Apulia (south-eastern Italy) and briefly described by
Caroli (1924) as representative of a new mysidacean genus. Almost at the same time,
a second genus and species, Lepidophthalmus servatus, was described by Fage (1924,
1925) from subterranean waters of Zanzibar (south-eastern Africa) as a representative of
the new family Lepidophthalmidae. However, the generic name created by him is a junior homonym of a decapod genus. Zimmer (1927) noted this homonymy and created
the replacement name Lepidops. Clarke (1961a) noted that this last name was again a
junior homonym of a decapod genus and created the second replacement name Lepidomysis. Finally, Ingle (1972) withdrew this last name in favour of its senior synonym,
Spelaeomysis Caroli, 1924. The invalid family name Lepidophthalmidae was twice replaced by family names based on junior homonyms of decapods, first by Lepidopidae
Stammer, 1933, and then by Lepidopsidae Villalobos, 1951, and finally became the still
valid name Lepidomysidae Clarke, 1961a. Meanwhile, Caroli (1937) had discovered a
highly aberrant mysidacean at the same groundwater localities as in 1924. He named it Stygiomysis hydruntina, by deriving the new genus name from the infernal river τυξ of the
ancient Greek and Roman mythologies. Based on this genus he defined a new family, Stygiomysidae. His discussion pointed to the considerably reduced carapace (figs. 54.1B,
54.3A; shorter than in Petalophthalmidae), the thoracopods 2-4 resembling gnathopods
(fig. 54.17C, D; as in Eucopiidae), the peculiar morphology of the uropodal sympods
(fig. 54.22F; reminiscent of those of the stomatopods), eyes reduced to plates, missing statocysts, and probably seven [actually four] pairs of oostegites as in [unlike] Spelaeomysis.
Disputes on the Mysidacea. – Accompanied by a number of additional modifications,
the unity of the Mysidacea within the superorder Peracarida was acknowledged by
most authors up to the 2000s (Norman, 1892; Calman, 1904; Holt & Tattersall, 1905;
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Hansen, 1910; Tchindonova, 1981; Nouvel et al., 1999). Nonetheless, Watling (1981,
1983, 1999), Schram (1984), Dahl (1992), Kobusch (1999), and Martin & Davis (2001)
had meanwhile developed a variety of alternative phylogenetic reconstructions by using
various methods of morphological analysis. Their conclusions had little in common
among each other, apart from doubting the unity of the order Mysidacea and placing
the Mysida and Lophogastrida as separate orders in various positions within or outside
the Peracarida, respectively. Nonetheless, more recent detailed morphological analysis
suggested a renaissance of the unity of the Mysidacea within the Peracarida (De JongMoreau & J.-P. Casanova, 2001; Richter & Scholtz, 2001; Wirkner & Richter, 2007, 2010).
Recent genetic analyses pointed again to a disunity of the Mysidacea. From rDNA sequence analysis, Jarman et al. (2000), Spears et al. (2005), and Meland & Willassen (2007)
obtained the Lophogastrida mostly within the Peracarida, but the Mysida elsewhere within
the Eumalacostraca, in any case distant from the Lophogastrida. In their analysis, Meland & Willassen (2007) included also two species of Stygiomysida, formerly considered
a suborder of the Mysida, and obtained the Stygiomysida closer to the Lophogastrida.
Jenner et al. (2009) compared and tested different methods of phylogenetic reconstruction and concluded that the published evidence could not satisfactorily resolve the
relationships between different higher taxa within the Eumalacostraca. This uncertainty is
reflected by the above-discussed pendular movements of mysidacean classification in the
1980-2000s. Irrespective of a potential unity or disunity of the Mysidacea, Richter (2003)
concluded a monophyly of the Lophogastrida from apomorphic characters of the mouthparts, and Wittmann (2013b) a monophyly of the Mysida based on the armature of the male
genital pores. Unless new evidence is presented, keeping the Lophogastrida, Stygiomysida,
and Mysida as different taxa at whatever level promises more stable systematics than any
kind of fusion.
Terminology and definitions
General terminology. – The present terminology essentially follows Tattersall & Tattersall (1951), with emendations by Băcescu (1940, 1954) and Ariani & Wittmann (2000).
For reasons of brevity, ‘mysids’ is here often used for Mysida, ‘lophogastrids’ for
Lophogastrida, ‘stygiomysids’ for Stygiomysida, and ‘mysidaceans’ for the conglomeration of Lophogastrida, Stygiomysida, and Mysida. The appendages along with their
segmental and setation patterns are distinguished as in figs. 54.10, 54.14, 54.18, 54.20,
54.21. In this context, ‘multi-segmented’ means more than two-segmented. Features of the
foregut are termed according to De Jong-Moreau & J.-P. Casanova (2001); synonyms used
by Kobusch (1998) are given in parentheses in the legend of fig. 54.29. Tagmata and body
segmentation are termed according to Gruner & Scholtz (2004) in the first volume of the
present series.
The terminology of stages within the moult cycle is given by Charmantier-Daures &
Vernet (2004) in the first volume of the present series. They essentially follow the system
of Drach (Drach & Tchernigovtzeff, 1967), but use the term ‘diecdysis’ instead of the
misleading ‘intermoult period’. This last term was previously more commonly used in the
mysid literature (Cuzin-Roudy & Tchernigovtzeff, 1985). Embryonic and larval stages
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(nauplioids, postnauplioids) in the marsupium are distinguished according to Wittmann
(1981a).
Taxonomy. – The families and subfamilies of the Lophogastrida, Stygiomysida, and
Mysida are acknowledged essentially according to Meland & Willassen (2007); for
taxonomic modifications of their scheme see ‘Systematics’ below. Wherever convenient,
taxa quoted by previous authors are cited in the currently valid form, for reasons of brevity
in most cases without additional indication of the originally quoted taxa.
Classification and metric measurements. – Literature data were readjusted, transformed and/or recalculated if they differed from the following scheme: Body size (mm)
is the distance from the anterior margin of the carapace to the end of the telson without
spines. Egg size (mm) is expressed as the geometric mean of apparent length and width of
the mostly sub-ellipsoid bodies. Degree of endemism is expressed according to Myers &
De Grave (2000). Salinity (S) is expressed as a dimensionless equivalent of electric conductivity, and the Venice System was used for salinity classification of water bodies (Por,
1972). The suffixes ‘-haline’ and ‘-saline’ are used for water bodies only, ‘-halophilic’ and
‘-halobious’ for biota (similar to Ziemann & Schulz, 2011).
Cuticle structures. – Beyond the classical distinction of setae and spines (Tattersall
& Tattersall, 1951), the ‘fringes’ (fig. 54.9C-E) are non-sensory cuticle structures found
in cumaceans by Klepal & Kastner (1980) and introduced for the study of mysids by
Wittmann & Ariani (1998). Similarly, Wittmann (1985) introduced the numbers and
arrangement of small pores (fig. 54.9F-H) on the carapace as diagnostic characters of
certain taxa of Mysida. ‘Fenestra paracornealis’ (Ariani & Wittmann, 2000) is a pale,
pigment free, rounded and slightly elevated spot (fig. 54.12D) dorsally on the eyestalks
near the cornea.
Thoracic endopods. – For the eight pairs of endopods (limbs), Tattersall & Tattersall
(1951) and many others distinguished two pairs of maxillipeds versus six pairs of
pereiopods. In contrast, Bowman (1977) and other, mainly American authors, emphasized
the second endopod as a pereiopod, thus counting seven pairs of pereiopods. Bowman
(1973) and Bowman et al. (1984) applied this scheme also for the two families of the
Stygiomysida, i.e., the Stygiomysidae and the Lepidomysidae, irrespective of different
numbers of maxilliped-like endopods. The different terminologies resulted in inconsistent
numbering of pereiopods, persisting up to the present in the literature. Gruner & Scholtz
(2004) located this problem widely in the malacostracan literature and therefore proposed
to use only the term ‘thoracopods’. We avoid ‘pereiopods’ also because the etymology
as ‘walking legs’ only marginally fits the behaviour of mysidaceans. The various taxa
sometimes use the thoracic endopods 3-8 for crawling, but among a greater diversity of
functions, mainly to form a filtration basket, to grasp and manipulate food, and/or to hold
onto the substrate.
The slenderness of thoracic endopods is evaluated by the ratio (R: Băcescu, 1940)
between the length and maximum width of the merus (sensu Tattersall & Tattersall, 1951;
this is the carpus sensu Băcescu, 1954) for certain endopods, particularly the sixth (R6 )
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or the seventh (R7 ) (arrows in fig. 54.18M; Ariani & Wittmann, 2000). The ‘propodal
formula’ shows, according to Ariani & Wittmann (2000), the variability in the number
of carpopropodal segments along the series of third to eighth thoracic endopods: ranges
are reported as “a-b” or “b-a” according to the prevailing frequency, and parentheses
indicate rare or exceptional values. For instance, the carpopropodus of thoracopods 3-8 in
Diamysis lagunaris is described with 3-2 (4), 2-3, 2, 2, 2, and 2 (3) segments, respectively.
‘Paradactylary setae’ (fig. 54.18O; Băcescu, 1940) are the usually two pairs of setae
positioned at the end of the propodus, and flanking the dactylus at its base, often showing
a peculiar morphology. Below the terminal claw 0-3 (mostly one) ‘subungulary setae’
(fig. 54.18O) may be present on the dactylus.
Features of the pleon. – Uniramous pleopods are identified according to W. M.
Tattersall (1951) as derivates of endopods (fig. 54.21S) if they show outwards (= laterally)
directed lobes (= exites = pseudobranchial lobes) or rudiments of such lobes. The term
‘scutellum paracaudale’ (fig. 54.22O) is used for the latero-dorsal plates protruding from
the sixth pleonite and flanking the telson (Ariani & Wittmann, 2000). Voicu (1974, 1981)
defined the ‘statolith formula’ according to the arrangement of pore groups and numbers
of pores within each group, in semicircular series at the surface of the statoliths (static
bodies), starting with the most caudal pores (a + b + c + d . . . ; Schlacher et al., 1992).
In the variant by Wittmann (1992a) this includes also variation (in parentheses) and total
numbers of pores, for example 2 + 3 + (4-10) + (2-4) + (3-6) = 18-24 in Mesopodopsis
aegyptia.
EXTERNAL MORPHOLOGY
Habitus
As typical for Malacostraca, the Lophogastrida, Stygiomysida, and Mysida — together
exposed in fig. 54.1 — share the ‘caridoid facies’. According to Calman (1909), this
facies is characterized by the presence of three tagmata, which are represented by a
five-segmented head (not counting a likely present ocular somite) fused with an eightsegmented thorax to form a cephalothorax, and by a six-segmented pleon. The following
features complete the ‘caridoid’ picture of a typical member in these orders: moveable
stalked eyes, biramous antennulae and antennae, a well-developed antennal scale, a
carapace enveloping the thorax, biramous thoracopods, mostly biramous male pleopods,
a ventrally flexing pleon capable of tail flipping, and a strong tail fan. In addition, the
adult females share a large brood pouch, whose large size strongly modifies the body
shape below the thorax. Both sexes of these orders also share a normally well-developed
carapace, dorsally adhering to all cephalic somites plus the anterior 1-4 thoracic somites,
and, with certain exceptions, projecting freely over some of the more posterior somites.
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Fig. 54.2. Habitus of females in the Lophogastrida families Gnathophausiidae (A), Lophogastridae
(B, C), and Eucopiidae (D). A, Gnathophausia ingens (Dohrn, 1870); B, Lophogaster typicus M.
Sars, 1857; C, Ceratolepis hamata G. O. Sars, 1883; D, Eucopia australis Dana, 1852. [After G. O.
Sars, 1885a.]
Lophogastrida (fig. 54.2). – The Gnathophausiidae show a comparatively rigid, keeled
carapace. In several species, particularly in Gnathophausia zoea, the carapace bears an
extremely long, toothed rostrum and a posterior spear-like prolongation (fig. 54.6C, D). As
a striking feature, the Eucopiidae show strong, subchelate thoracic endopods 2-4, strongly
contrasting with the very thin, elongate, weakly subchelate endopods 5-7 (fig. 54.2D).
Stygiomysida (fig. 54.3). – All species show at least some degree of eye reduction,
indicative of their typically subterranean mode of life. Within this order, only Spelaeomysis shows a relatively ‘normal’ mysidacean habitus, the exception being a terminally
rounded, subtriangular to semi-circular, anterior projection (fig. 54.3B) from the penultimate thoracic somite. This large, striking flap, also termed a ‘scale’, overlaps with the
postero-median margin of the carapace from behind. There is no such scale in Stygiomysis,
which is characterized by a vermiform body (figs. 54.1B, 54.3A) and a strongly shortened,
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Fig. 54.3. Habitus of the Stygiomysida families Stygiomysidae (A) and Lepidomysidae (B-D).
A, Stygiomysis cokei Kallmeyer & Carpenter, 1996, dorsal; B, lateral aspect of Spelaeomysis
cardisomae Bowman, 1973, most appendages omitted, arrow shows anterior lobe of ultimate thoracic
tergite; C, ‘face’ of Spelaeomysis bottazzii Caroli, 1924, in lateral view; D, lateral aspect of
laboratory-kept Spelaeomysis bottazzii bearing nauplioid larvae. [A, after Kallmeyer & Carpenter,
1996; B, after Bowman, 1973; C, after Inguscio, 1998; D, photo Antonio P. Ariani.]
reduced carapace, posteriorly not extending beyond the fusion zone with the four anterior thoracomeres. According to in vivo observations by Inguscio (1998), the slender body
form enables this highly specialized, stygophilic animal to perform very quick movements
with abrupt direction changes of almost 90°. We interpret this as being advantageous for
locomotion through the ‘tunnel’-network of meso-interstitial groundwater habitats. Correspondingly, we consider the absence of a free posterior margin of the carapace in Stygiomysis, as well as the protection of the free margin by a flap of the penultimate thoracomere
in Spelaeomysis, as adaptations to prevent hooking the carapace on the wall of narrow
‘tunnels’ upon backwards movements. Such movements appear necessary at least when
the animal reaches a dead end.
Mysida (figs. 54.4, 54.5). – Most species show a fully ‘normal’ mysidacean habitus.
There are varying degrees of eye modifications, mostly eye reductions, in most subterranean and also in many marine, meso- to bathypelagic species. Some holopelagic forms
show an elongate trunk, either by elongation of certain thoracomeres (fig. 54.5G) or of
the pleon (see below, ‘Cephalothorax’). In several pelagic genera, particularly Caesaromysis (fig. 54.12C) and Echinomysis, the carapace and most pleomeres bear great numbers
of long spiniform processes, giving these animals a hedgehog-like appearance. Unlike all
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Fig. 54.4. Habitus of males in the Mysida families Petalophthalmidae (A) and Mysidae (B-M),
the latter represented by all ten of its acknowledged subfamilies: Boreomysinae (B), Rhopalophthalminae (C), Siriellinae (D), Gastrosaccinae (E, F), Erythropinae (G), Leptomysinae (H),
Mysinae (J), Palaumysinae (K), Mysidellinae (L), and Heteromysinae (M). A, Petalophthalmus
armiger Willemoës-Suhm, 1875; B, Boreomysis obtusata G. O. Sars, 1884; C, Rhopalophthalmus egregius Hansen, 1910, arrow points to the pleural plate of the first pleomere; D, Siriella
thompsonii (H. Milne Edwards, 1837); E, Anchialina truncata (G. O. Sars, 1883); F, Haplostylus
lobatus (H. Nouvel, 1951); G, Amblyopsoides crozetii (Willemoës-Suhm in G. O. Sars, 1884);
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remaining Mysida, several genera of the Gastrosaccinae are capable of digging and seemingly have a posteriorly elongated marsupium (fig. 54.5F). Actually, the elongation is due
to a pair of large pleurites projecting from the first pleomere and supporting the posterior
part of the marsupium from the side and from behind. This support may serve in brood
protection when the mothers bury themselves up to 5 cm into the sediment.
Size of adults
Mysida. – Typical adult body lengths of epipelagic and coastal species are 3-8 (range
1-17) mm in tropical, 6-15 (3-50) mm in temperate, and 10-30 (4-77) mm in Arctic
zones. The increase of body size with increasing latitudes is discussed in ‘Growth’
below. Bathypelagic species are 8-35 (6-85) mm long. Except in a few species, adult
males are on average smaller than females, mainly due to earlier attainment of sexual
maturity, shorter life span, and/or smaller moult increments after attainment of adulthood
(Murano, 1964b, 1999b; Clutter & Theilacker, 1971; Hakala, 1978; Hanamura, 1999). The
largest Mysida species, Birsteiniamysis inermis from the boreal North Atlantic, reaches
up to 85 mm (Mauchline & Murano, 1977). This species is characterized by strong
size variations between different geographical localities. Marked seasonal size differences
are observed in many species. For instance, off Arcachon (France), adult Schistomysis
spiritus are larger in winter than in autumn. Seasonal differences in relative dimensions
(cyclomorphosis) of appendages were also described; on this basis, Wittmann (1992b)
identified Siriella adriatica as the overwintering generation of Siriella gracilipes. Adult
sizes of mysids typically decrease with increasing temperature (i.e., warmer season or
climate) due to earlier attainment of sexual maturity and reduced longevity, despite the fact
that daily growth rates increase with increasing temperature, e.g., in Neomysis intermedia
(cf. Toda et al., 1983a, 1984).
Lophogastrida and Stygiomysida. – Body sizes of adults range from 6 to 39 mm in
Lophogastridae, 27-66 mm in Eucopiidae, and 40-351 mm in Gnathophausiidae. The
maximum size was found by Clarke (1961b) in Gnathophausia ingens (fig. 54.2A).
According to J.-P. Casanova (1996a), the females of Paralophogaster glaber showed
maximum sizes of 21.5 or 33 mm when collected near the Indonesian islands Kai
and Tanimbar, respectively, despite a relatively small distance of only 300 km between
these islands. Among adult Stygiomysida, the Lepidomysidae measure 3-11 mm, the
Stygiomysidae 5-21 mm.
H, Leptomysis gracilis (G. O. Sars, 1864); J, Diamysis cymodoceae Wittmann & Ariani, 2012; K,
Palaumysis philippinensis Hanamura & Kase, 2002; L, Mysidella typhlops G. O. Sars, 1872; M,
Heteromysis harpaxoides Băcescu & Bruce, 1980. [A, B, D, E, G, after G. O. Sars, 1885a; C,
after O. S. Tattersall, 1952; F, after Tattersall & Tattersall, 1951; H, L, after G. O. Sars, 1879; J,
after Wittmann & Ariani, 2012a; K, after Hanamura & Kase, 2002; M, after Daneliya, 2012; A-M,
modified.]
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Fig. 54.5. Habitus of females in the Mysida families Petalophthalmidae (A) and Mysidae (B-M),
the latter represented by all ten of its acknowledged subfamilies: Boreomysinae (B), Rhopalophthalminae (C), Siriellinae (D), Gastrosaccinae (E, F), Erythropinae (G), Leptomysinae (H), Mysinae
(J), Palaumysinae (K), Mysidellinae (L), and Heteromysinae (M). A, Hansenomysis falklandica
O. S. Tattersall, 1955; B, Birsteiniamysis inermis (Willemoës-Suhm, 1874); C, Rhopalophthalmus
tartessicus Vilas-Fernández, Drake & Sorbe, 2008; D, Siriella thompsonii (H. Milne Edwards, 1837);
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Carapace
Gross structure and formation. – In the Lophogastrida, Stygiomysida, and Mysida, the
carapace adheres to the cephalothorax from the tergite of the antennal somite backwards
over the region of the mouthparts and over 1-4 anterior thoracic somites. Along its
margins the carapace — during larval growth — drives backwards, like a wedge, those
hemi-tergites and pleurites belonging to somites not directly contributing to carapace
formation (B. Casanova, 1987, 1991), at least in Lophogastrida and Mysida (figs. 54.6A,
B, 54.8D). The epimeron, a membranous structure lining the carapace inside, is laterally
linked with the exoskeleton of the cephalothorax (fig. 54.8A-C). The remaining posterior
thoracomeres may be covered by the carapace, but all of them are free and distinct.
During larval development the posterior progression of the carapace leads to dorsal
opening of the tergites of the cephalic somites and, in Gnathophausiidae, of half of the
first thoracic somite. The cephalic tergites plus the anterior 3.5 thoracic tergites become
opened in Lophogastridae, Eucopiidae, and Mysidae (B. Casanova et al., 2002). The larval
genesis of the carapace has not yet been studied in Petalophthalmidae, Lepidomysidae,
and Stygiomysidae.
Rostrum and analogous structures. – Anteriorly, the carapace is produced into a
frontal shield (rostrum) which may be pointed (figs. 54.2A, 54.6C, D, F), rounded (fig.
54.7D, H), or rarely absent. This shield represents a prolongation of the antennal tergite
(fig. 54.6A, B; B. Casanova, 1991). In several genera of Mysinae (Mysida: Mysidae),
1-2 subrostral processes project anteriorly from the antennal somite, emerging between
the ocular symphysis and the carapace. In the mostly Ponto-Caspian genera Paramysis,
Caspiomysis, Katamysis, and in others, the subrostral process extends anteriorly beyond
the true rostrum if there is one. In several species, most strikingly in Paramysis ullskyi and
Paramysis inflata, there is a well-formed subrostrum, whereas a true rostrum is completely
missing. Particularly in the Gastrosaccinae, one may find large suborbital median processes
emerging between the ocular and the antennular symphyses. Such species may show up to
three rostrum-like anterior projections (fig. 54.7D).
In the Lophogastrida genus Gnathophausia there is a strong triquetrous rostrum with
serrated edges (figs. 54.1A, 54.6C, D). In the Lophogastridae and Gnathophausiidae, the
rostrum usually shows oblique longitudinal ridges, often elongated by strong spines (in
certain species of Gnathophausia). These spines are most strongly developed in juveniles
and may be serrated (fig. 54.6C). The Eucopiidae have either no rostrum or a mostly short,
anteriorly well-rounded rostrum with bare margins. In addition, there is always a distinct,
E, Anchialina truncata (G. O. Sars, 1883); F, Gastrosaccus spinifer (Goës, 1864); G, Longithorax
fuscus Hansen, 1908, thoracic endopods not shown; H, Leptomysis gracilis (G. O. Sars, 1864); J,
Praunus flexuosus (O. F. Müller, 1776); K, Palaumysis simonae Băcescu & Iliffe, 1986; L, Mysidella
typica G. O. Sars, 1872; M, Heteromysis wirtzi Wittmann, 2008. [A, after O. S. Tattersall, 1955; B,
D, E, after G. O. Sars, 1885a; C, after Vilas-Fernández et al., 2008; F, after Wittmann et al., 2011; G,
after Tattersall & Tattersall, 1951; H, J, L, after G. O. Sars, 1879; K, after Hanamura & Kase, 2002;
M, from the illustration by Wittmann on the cover of Crustaceana, vol. 86, 2013; A-M, modified.]
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anteriorly directed process, commonly termed ‘pseudorostrum’. This process emerges
below the ocular symphysis and probably pertains to the antennular somite, ergo not to
the antennal somite as in the Lophogastridae and Gnathophausiidae (fig. 54.6A, B).
External structures of the carapace. – The carapace is mostly thin and membranous, or
somewhat calcified only in certain Lophogastridae (figs. 54.2B, 54.6F) and Gnathophausiidae (figs. 54.2A, 54.6C, D). The carapace of the Lophogastrida and Stygiomysida, and
in most species of Mysida, shows a distinct transverse furrow (= cervical sulcus; figs.
54.2B, 54.7E, F, 54.9F, G) approximately above the mandibles. This furrow is completely
missing in certain taxa of Heteromysinae. In some species of Lophogaster the surface of
the carapace may be granulose (fig. 54.6F) or uniformly finely carved (Fage, 1942; J.-P.
Casanova, 1993, 1997). In the Mysinae genus Diamysis, the morphology and distribution
of ‘fringes’ (as defined above; figs. 54.7C, 54.9C-E) on the carapace are of great value
in defining different species (Wittmann & Ariani, 1998, 2012a, b; Ariani & Wittmann,
2000). Fringes of spectacular length are found (Wittmann & Ariani, 2012a) in Diamysis
cymodoceae. Similarly, submedian lobes (fig. 54.7E) and fringe-like processes (not fringes
sensu Klepal & Kastner, 1980) from the terminal margin of the carapace show a large diversity, which is useful for species definitions in the genera Gastrosaccus and Haplostylus
(Gastrosaccinae). The posterior margin of the carapace is generally emarginated, leaving
1-2 (range 0.5-3) ultimate thoracic somites exposed. In this manner, the carapace forms
two backwards directed lobes covering most of the thorax in lateral view. The ultimate
thoracic somite, however, remains laterally uncovered in many species of Siriellinae (figs.
54.4D, 54.5D); even more somites of the elongated thorax in Longithorax (Erythropinae)
remain uncovered (fig. 54.5G).
The branchiostegal carapace. – The Lophogastrida clearly show a branchiostegal
carapace (fig. 54.6E) in that the carapace cavity serves to protect the gills, which arise
from the coxae of the thoracic appendages (figs. 54.6E, G, 54.16C, E, G). Nonetheless,
one of the typically four gills of a given thoracopod is often directed inwards to the
ventral midline of the body (fig. 54.6E), i.e., away from the carapace cavity. Some of the
posterior gills may also project laterally out from the carapace cavity in large specimens
of Eucopiidae (fig. 54.6G). According to Wirkner & Richter (2013), the inner lining of
the carapace duplicature in Lophogaster typicus shows a similar network of haemolymph
channels as in the carapace of the Mysida discussed below. Lophogaster is well equipped
with branchiae, raising the question about what the function of this lining might be:
in analogy to ultrastructural findings of Kikuchi & Matsumasa (1993) in the estuarine
tanaid Sinelobus stanfordi, Wirkner & Richter (2013) proposed a mainly osmoregulatory
function of this lining. A certain osmoregulatory capability is generally found in waterborne respiratory tissue. In Sinelobus stanfordi, the ultrastructural features of the branchial
versus branchiostegal epithelia point to different functions in osmoregulatory ion transport,
in each case in addition to the respiratory function (Kikuchi & Matsumasa, 1993).
Based on these considerations and on the strictly euhaline distribution of Lophogaster,
it is premature to venture proposing a major osmoregulatory versus a minor respiratory
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Fig. 54.6. The carapace of the Lophogastrida families Gnathophausiidae (A, C, D), Lophogastridae
(B, E, F), and Eucopiidae (G). A, A’, schematic outline of the extension of the carapace and the
epimeres (dotted) in Gnathophausia Willemoës-Suhm, 1873, dorsal (A) and lateral (A’) aspects; B,
B’, the same for Lophogaster M. Sars, 1857; C, detached carapace of a juvenile Gnathophausia
ingens (Dohrn, 1870), inner ventral face; D, same species as before, carapace of a more advanced
juvenile, lateral; E, cross section between two consecutive thoracic appendages in Lophogaster
typicus M. Sars, 1857, showing the arrangement of branchiae; arrows indicate respiratory water
flow; F, Lophogaster pacificus Băcescu, 1985, dorso-lateral; G, Eucopia sculpticauda Faxon, 1893,
note that the carapace leaves some of the posterior gills exposed in lateral view. Abbreviations
indicate somites of the cephalothorax: a1, antennula; a2, antenna; md, mandible; mx1, maxillula;
mx2, maxilla; t1 to t8, thoracomeres 1 to 8. [A, B, after B. Casanova, 1991; C, D, after G. O. Sars,
1885a; E, after Manton, 1928a, and Nouvel et al., 1999; F, after Băcescu, 1985; G, after Tattersall &
Tattersall, 1951; E-G, modified.]
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Fig. 54.7. The carapace of the Mysida (A-G) and the Stygiomysida (H, J): examples for the
families Petalophthalmidae (A, B), Mysidae (C-G), Lepidomysidae (H), and Stygiomysidae (J).
A, Hansenomysis abyssalis Lagardère, 1983, lateral; B, Hansenomysis nouveli Lagardère, 1983,
dorsal; C, Diamysis bahirensis (G. O. Sars, 1877), carapace expanded (flattened) on slide, dorsal; D,
rostrum and analogous processes in female of Gastrosaccus roscoffensis Băcescu, 1970; E, male of
previous species, carapace flattened as in (C), dorsal; F, Chunomysis diadema Holt & Tattersall, 1905,
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function of the branchiostegal epithelia. A definite conclusion will require appropriate
physiological data.
The respiratory carapace (fig. 54.31D). – The Stygiomysida and Mysida lack gills, but
the inner surface of the freely projecting parts of the carapace, i.e., the wall of the carapace
cavity, is lined with respiratory tissue. Wägele (1994) and Kobusch (1999) termed this a
‘respiratory carapace’. The respiratory lining is most striking in certain Gastrosaccinae.
As an example of an opposite development, in the stygobiotic Stygiomysidae the posterior
parts of the carapace are reduced, and the lateral carapace cavities are shortened (fig.
54.3A); this is not the case in their also stygobiotic relatives, the Lepidomysidae (fig.
54.3B). The reduction of the respiratory tissue together with the carapace in the former
are interpreted above (‘Habitus’) as a consequence of acquiring a vermiform body,
adaptive for locomotion in underground habitats. A posteriorly shortened, but less reduced
carapace cavity is found in the tropical, marine, cave-dwelling genus Palaumysis (Mysidae:
Palaumysinae; figs. 54.5K, 54.7G). These mysids have large, functional eyes and a
comparatively stout body. The degree of carapace reduction varies between the various
species of this genus (Hanamura & Kase, 2003). We conclude, that the reduced respiratory
surface in Palaumysis is a consequence of dwarfing. In most species of this genus, the
females grow to about the lower limit of body length (1 mm) required for successful
incubation of their relatively large larvae (see below, ‘Egg size’).
Cephalothorax
Metameric patterns. – According to Hansen (1925) the unpaired mobile elements
(“one” in Gnathophausia, two in Boreomysis and Mysis) in front of the cephalic region
may represent ocular and antennular somites, perhaps comparable to those in stomatopods.
Actually, examination of the internal cuticular organization of the cephalothorax showed
that tergites of the ocular as well as the antennular somites (fig. 54.8) are present in
Gnathophausia zoea, yet the tergite of only the antennal somite contributes to carapace
formation (B. Casanova, 1987, 1991). The posterior thoracic somites, not attached to the
carapace, are dorsally, laterally, and particularly ventrally well distinguished (figs. 54.6A,
B, 54.8A, C, D) in Lophogastrida and Mysida. They show a similar development except
for a strong elongation of certain thoracic somites in a few essentially holopelagic genera
belonging to the family Mysidae: the first somite in Arachnomysis or the eighth somite in
Longithorax (fig. 54.5G) and Gymnerythrops.
dorsal; G-J, different degrees of coverage of the cephalothorax by the carapace, as exemplified by
Palaumysis philippinensis Hanamura & Kase, 2002 (G, most setae omitted), Spelaeomysis longipes
(Pillai & Mariamma, 1964) (H) and Stygiomysis aemete Wagner, 1992 (J), anterior body regions
in dorsal view. Abbreviations: cp, cardial pore group; cv, cervical pore group; fr, fringes; ro, rostral
process; so, suborbital process; sr, subrostral process; tt4, tt8, thoracic tergites. [A, B, after Lagardère,
1983; C, after Wittmann & Ariani, 2012a; D, E, after Wittmann et al., 2011; F, after Tattersall
& Tattersall, 1951; G, after Hanamura & Kase, 2002; H, after Pillai & Mariamma, 1964; J, after
Wagner, 1992; A-J, modified.]
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209
Sternal projections. – Most Lophogastrida and certain Mysida show mostly unpaired
median projections from thoracic sternites, often equipped with scales or hairs. The
presence and structure of these sternal projections commonly differ between age stages
and/or sexes. In those species with distinct sternal projections in adult males (figs.
54.15N, 54.20F, 54.35A, D, E), one typically finds some projections also in juveniles
(fig. 54.35C) of both sexes, but no such projections or only rudiments in adult females
(figs. 54.15M, 54.35B). Less frequently, the situation is inverse: several species of Mysidae
show large foliaceous sternal processes, projecting from the ultimate thoracomere in adult
females only. These unpaired processes probably contribute to the posterior closure of the
marsupium (see below, ‘Oostegites’).
Pleon
Unlike Isopoda and Amphipoda, and certain taxa within the Decapoda, the pleon is
never reduced. Rather, it is always well developed and capable of emergency tail flipping
in the Lophogastrida, Stygiomysida, and Mysida. The five anterior pleonites are generally
similar in size; only the sixth is typically distinctly longer.
Lophogastrida. – Unlike in the family Eucopiidae (figs. 54.2D, 54.19A), all pleonites
in the Lophogastridae (fig. 54.2B) and Gnathophausiidae (fig. 54.2A) are flanked by
distinctly projecting, rounded or terminally pointed pleural plates. In these families the
sixth pleonite shows a more or less distinct transversal groove imitating an additional
segmental border (fig. 54.2A, B). This insinuates that the sixth pleonite may have
originated from the fusion of two ancestral somites as still found in the Leptostraca.
Interestingly, the ultimate pleonite lacks appendages in the Leptostraca, whereas its
posterior margin bears the uropods in the Lophogastrida. According to Manton (1928a) the
embryonic development and the arrangement of the musculature favour the hypothesis of
two fused somites. Finally, the sternites show non-dimorphic, median, spiniform processes
in Lophogaster.
Stygiomysida. – The pleura of the pleon lack conspicuous plate-like extensions in
both families of this order. The sympods of pleopods 3-5 are bilaterally connected by a
series of transverse, membrane-like sternal lamellae. These lamellae may incorporate the
sympods (Stygiomysis holthuisi; fig. 54.17L; Gordon, 1960) or leave the sympods separate
(Spelaeomysis cardisomae; fig. 54.17M; Bowman, 1973).
Fig. 54.8. Internal cuticular organisation of the cephalothorax in Lophogastrida (A, B) and Mysida
(C, D). A, Gnathophausia zoea Willemoës-Suhm, 1873, dorsal view after median exposure of the
tergites; B, C, Lophogaster typicus M. Sars, 1857 (B) and Boreomysis microps G. O. Sars, 1883 (C),
lateral view after removal of the right body half; D, thorax of the postnauplioid stage of Praunus
flexuosus (O. F. Müller, 1776) in lateral view, arrow points to the posterior suture of the carapace at
the junction between the numbered thoracic somites 3 and 4. Abbreviations: ac, arthrodial cavities; c,
carapace; e, epimeres; md, mandible; mxl, maxillula; ta1, antennular tergite; tmx2, maxillary tergite;
to, ocular tergite; t1-t8, thoracic somites 1-8. [A-C, after B. Casanova, 1991; D, after B. Casanova et
al., 2002, with permission by “© Canadian Science Publishing or its licensors”, Ottawa.]
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Mysida. – Conspicuously projecting pleural plates on the pleon are rare in this order.
The females of Gastrosaccinae show pleural plates on the first pleonites, supporting the
marsupium from the side and from behind (fig. 54.5F). Unlike in other genera of this
subfamily, in Archaeomysis such plates are also present in males, but smaller. In certain
species of this genus, both sexes show additional plates decreasing in size from pleomere
2 to 5. Also Rhopalophthalmus (Rhopalophthalminae) shows ventrally projecting pleural
plates on the first pleonites, but only in the males (arrow in fig. 54.4C). In several
species of Mysinae, e.g., most distinctly in Paramysis portzicensis, the pleonites show
transversal folds simulating double somites. In a number of Mysinae (Mysidae) the telson
is flanked by latero-dorsal plates (scutella paracaudalia; fig. 54.22O), protruding from
the sixth pleonite. The scutella are important for the diagnosis of Diamysis species (Ariani
& Wittmann, 2000). In embryos of Mysida, rudiments of a seventh pleon somite are
indicated by the appearance of separate sixth and seventh ganglia during the development
of Hemimysis and Mesopodopsis (Manton, 1928b; Nair, 1939).
Telson
The trunk ends in a dorsoventrally flattened telson (fig. 54.22D), ventrally bearing the
anus (fig. 54.22F) in sub-basal position. Apart from this, the telson shows a great variability
in form and armature between the various taxa from order down to species level. It may be
linguiform, semi-ellipsoidal, triangular, but mostly trapezoidal, often with a more or less
incised terminal margin.
Lophogastrida (fig. 54.22A-E). – The Eucopiidae and Lophogastridae show a roughly
linguiform telson whose margins are armed with spines at least on the terminal half.
The telson of Eucopia sculpticauda is exceptional by two subapical constrictions. In
most species of Lophogaster and Paralophogaster the terminal margin of the telson
shows a small, transverse, median portion between a pair of large apical spines; this
portion bears a few laminae with barbed setae in-between (fig. 54.22A). The telson of
the Gnathophausiidae has two long, longitudinal keels on the dorsal surface. Its small,
crescent-shaped terminal part is separated by a strong subapical constriction (fig. 54.22D).
Stygiomysida (fig. 54.22F-H). – All taxa show a comparatively short, linguiform to
trapezoid telson. At least the terminal margin, mostly also part of the lateral margins
(usually their distal parts) are armed with spines. In several species of Spelaeomysis, one
or more barbed setae are present on either side of the medio-apical spine (fig. 54.22H).
Mysida (fig. 54.22J-O). – The terminal incision, if present, of the telson is generally
armed with spine-like laminae, less frequently with (additional) spines, or again less
frequently there are only bare margins. The lateral margins are generally armed with
spines all along, or only along part of their length, but they may be completely smooth
in a few taxa. Fine hairs may be present in the space between these spines, particularly in
Mysinae, e.g., the genera Paramysis and Neomysis. The tip of the telson is often equipped
with a pair of plumose or barbed setae, particularly in Siriellinae (fig. 54.22L). Such
setae insert on the bottom of the telson cleft in a number of Leptomysinae genera, e.g.,
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Doxomysis, Prionomysis, and Tenagomysis. Rarely there may be a brush of plumose setae
on the ventral face of the telson, as in the Leptomysinae genera Notomysis from coastal
waters of India and Australia, and the closely related Antichthomysis from Tasmania.
In the Rhopalophthalminae, the terminal margin of the telson is always armed with
four large, microserrated spines. In the Petalophthalminae genera Petalophthalmus (fig.
54.22J), Parapetalophthalmus, and Pseudopetalophthalmus, the median portion of the
terminal margin of the telson is lined with spine-like laminae, and the lateral portions
by a number of barbed (microserrated) setae (spines).
Integument and colour
Cuticular structures. – The body surface of the Lophogastrida, Stygiomysida, and
Mysida appears generally smooth, not considering structures <2 μm. Nonetheless, in
certain taxa, scales, hairs, spines, or burls may be present on limited regions of the body.
In a few Mysida, such as Acanthomysis longicornis and Leptomysis gracilis, most of the
cuticle is covered by small scales, giving the entire body a hispid appearance. In most
taxa, however, such scales show a more restricted distribution on the body wall and/or the
appendages (fig. 54.9J, K). In the males of certain Diamysis species, part of the carapace
may be covered by fringes, i.e., hair-like non-sensory cuticular structures; these fringes
are strikingly long and densely arranged in Diamysis cymodoceae (fig. 54.9C-E; Wittmann
& Ariani, 1998, 2012a, b; Ariani & Wittmann, 2000).
In addition to the integumental sensilla that occur on various appendages, all pelagic
crustaceans examined by Mauchline (1977) after treatment with potassium hydroxide
showed small ‘pores’ (sensu lato; 1-20 μm) related to sense organs or to glands. These
pores are present on the body wall and in most taxa also on the carapace. Mauchline
(1977) found a median group of four larger pores dorsally near the posterior margin of
the carapace in the lophogastrid Eucopia sculpticauda. Each lateral pair is connected by
series of smaller pores, together forming a compound organ with a thin central area (fig.
54.9A). According to Mauchline (1977) this organ may be analogous to the compound
organs with unknown function on the carapace of the nebaliacean Nebaliopsis typica.
Mauchline (1977) and Wittmann (1985 and later) noted small pores (1-4 μm) on the
dorsal face of the carapace, the pleon, and on dorsally uncovered thoracomeres in many
species of Mysidae (Mysida). These pores show species-specific distribution patterns and
are of taxonomic value. The Leptomysinae and Mysinae often bear a dense group of
pores near the median, posterior margin of the carapace (fig. 54.9H); often there is also
a transverse row in cardial position (fig. 54.9B, C, F), in most cases arranged in two
symmetrical subgroups; and slightly less frequently a mostly small group in cervical
position (fig. 54.9C, F, G). These groups, especially the posterior group, also occur in
certain Erythropinae and Heteromysinae, but otherwise numbers and distribution of pores
are more variable in these subfamilies. SEM-observations in Diamysis bacescui revealed
two types of pores: the cardial and cervical pores resemble plant stomata due to their liplike margins, whereas the remaining, more widely scattered ones are generally smaller and
have a more simple, rounded opening (Wittmann & Ariani, 1998).
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Fig. 54.9. Cuticle structures on the carapace and the tergites of the trunk in Lophogastrida (A)
and Mysida (B-K), dorsal views only. A, B, pores (sensu lato) in the integument of the carapace,
several posterior thoracomeres and all pleomeres after treatment with potassium hydroxide (KOH),
Eucopia sculpticauda Faxon, 1893 (A) and Praunus flexuosus (O. F. Müller, 1776) (B); C, pores and
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Colour (fig. 54.1). – For the nature of crustacean pigments and chromatophores,
see the first volume of the present series (Noël & Chassard-Bouchaud, 2004). Most
bathypelagic mysids are more or less uniformly red with purple, orange, violet, or rarely
nigrescent (Longithorax fuscus) tinge. The benthopelagic and littoral species are rarely
colourless or uniformly coloured. Most show a more or less dense cover by ramifications of
chromatophores containing black, brown, or red pigment. There may also be substances
giving white, yellow, or blue reflections. The patterns and action of the chromatophores
produce a mostly spotted aspect, varying with illumination and colour patterns of the
substrate. Nonetheless, the colour patterns also show specific components useful for visual
distinction of species. Many species exhibit a longitudinal dorsal stripe, which may be
darker or, in contrast, lighter than the rest of the body. Numbers, distribution and, in certain
cases, colour of the chromatophores may be of taxonomic value. Thus, the striking and
constant difference in colour (red and black, respectively) of the dorsal chromatophores
gave first hints to the splitting of Diamysis lagunaris from Diamysis mesohalobia, two taxa
that were long taxonomically confused (Ariani & Wittmann, 2000: fig. 2D-F). The semihypogean species Diamysis camassai shows a darker pigmentation in summer compared
to winter and to its epigean congeners, probably to avoid light damage upon migration
from dark to light parts of its habitat (Ariani & Wittmann, 2002). Certain pigment cells
are found in the hypodermis, others on or close to the surface of internal organs such
as those pertaining to the nervous system, stomach, and gonads (Keeble & Gamble, 1904;
Degner, 1912a, b). Often the chromatophores appear strongly ramified, as those present on
the telson and oostegites in several species of Diamysis and Paramysis. It is noteworthy
that Costa (1847) already remarked on the ramifications visible on the oostegites in his
description of Acanthomysis longicornis from the Gulf of Naples, but oddly considered
them as pertaining to the circulatory system. The cornea varies from red to brown or black,
rarely blue (Mesopodopsis slabberi), often with metallic bronze or golden reflection.
Important components of the body colour are often not related to pigment cells. Such
colours are due to stomach and intestine contents, to the colour of eggs in the ovaries and/or
in the marsupium, and to yellow to orange-red fat bodies (oil globules) visible through the
more or less transparent body wall. In certain species the entire cuticle (Heteromysis) or
only that of setae (Praunus) may show a violet tinge. In coastal Mysidae, the eggs or their
yolk are mostly pale to yellow or orange, but also red, green, blue, or violet. In Leptomysis
fringes on the carapace of male Diamysis cymodoceae Wittmann & Ariani, 2012, carapace expanded
(flattened) on slide, dorsal; D, detail of (C) showing the fringes; E, detail from another specimen, like
(D), showing a dense fur formed by fringes; F, carapace with three major pore groups as typical for
species of Leptomysis G. O. Sars, 1869; G, cervical pore group in female Leptomysis mediterranea
G. O. Sars, 1877; H, mid-terminal pore group located on a slight elevation directly in front of the
carapace margin in male Leptomysis posidoniae Wittmann, 1986; J, scales and setae on the basis
of the terminal segment of the antennular peduncle in female Leptomysis buergii Băcescu, 1966;
K, scales covering the eyestalk in a female Leptomysis posidoniae. Abbreviations: cp, cardial pore
group; cpo, compound organ sensu Mauchline (1977); cs, cervical sulcus; cv, cervical pore group;
fr, fringes; mtp, medio-terminal pore group. [A, B, after Mauchline, 1977; C-E, after Wittmann &
Ariani, 2012a; F-K, after Wittmann 1986a, b; A-C, F, H, modified.]
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the colour of yolk appears to be related to the habitats in which the species live (Wittmann,
1981a). The eggs of several Heteromysis species are brilliantly green (visible through the
transparent carapace in fig. 54.1D), strongly contrasting with the predominantly orangered body colour of the incubating mothers (Wittmann, 2008; Daneliya, 2012).
Cephalic appendages
Antennula (figs. 54.10A, B, 54.11A, B, 54.12A-G). – The antennules show a threesegmented peduncle with two unequal, multi-segmented flagella equipped with a variety
of sensory setae. The inner flagellum is generally shorter than the outer in Lophogastrida
(fig. 54.1A) and Mysida (figs. 54.4, 54.5), but not so in the Stygiomysida family
Lepidomysidae (fig. 54.3A). Compared to females, the male flagella are mostly larger and
more robust, often with different sets of sensory setae; these differences are most striking
in Hansenomysis (Petalophthalmidae: Hansenomysinae). The males of Mesopodopsis and
Surinamysis (Mysidae: Mysinae) show a long, unsegmented lobe resembling a third,
rudimentary flagellum. In most Mysidae males, the distal segment of the peduncle bears
a conical or subcylindrical (rarely sub-globular), inwards and/or forward to backwards
directed process with a brush of sensory setae (fig. 54.12C, E, G). This process is
commonly termed appendix masculina (see below, ‘Sexual dimorphism’). In males of
certain Heteromysinae this appendix may be very short, rarely absent, but always shows
the brush of setae typical for males in the family Mysidae (see below, ‘Sensory setae’).
The antennular peduncle is usually more stout in males (fig. 54.12E) than in females (fig.
54.12F). In most species it shows additional dimorphic elements regarding lobes, spines
and/or setae.
Antenna (figs. 54.10C-G, 54.11B, D, 54.12A-D, H-L). – The antennal sympod
consists of three often poorly discernible segments. In the Mysida, the end sac (fig.
54.12L) of the antennal gland is generally large and may be confused with a segment.
The sympod bears a plate-like exopod (= antennal scale) and a multi-segmented endopod.
The endopod shows a somewhat robust trunk (= antennal peduncle) composed of 3-4
segments, with a long multi-segmented flagellum. The antennal scale varies greatly in
form and size between the taxa (fig. 54.12A-D, H-L). It may be unsegmented or show a
Fig. 54.10. Antennae and mouthparts in the Lophogastrida families Gnathophausiidae (A, C, G-K,
M, O), Eucopiidae (B, D, L, N), and Lophogastridae (E, F). A, antennula with eye and rostrum
in Gnathophausia longispina G. O. Sars, 1883; B, the same for Eucopia australis Dana, 1852; C,
antenna of Gnathophausia ingens (Dohrn, 1870); D, antenna of Eucopia australis; E, antenna of
Lophogaster typicus M. Sars, 1857; F, antenna of Ceratolepis hamata G. O. Sars, 1883; G, antenna of
Gnathophausia longispina G. O. Sars, 1883; H, labrum and mandibles in Gnathophausia longispina;
J, detail of (H) showing the masticatory surface of the mandibular trunk, posterior face; K, labium
(paragnaths) of Lophogaster typicus, anterior face; L, maxillula of Eucopia australis; M, maxillula
of Gnathophausia longispina; N, maxilla of Eucopia australis; O, maxilla of Gnathophausia
longispina. Abbreviations: ba, basis; cx, coxa; ed, endite; end, endopod; ex, exopod; lo, luminescent
organ; pcx, praecoxa; pl, retroverted palp. [A-J, L-O, modified after G. O. Sars, 1885a; K, original
drawing of an adult male with 20 mm body length from Hjeltefjord (Norway).]
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216
Fig. 54.11. Antennae and mouthparts in the Stygiomysida families Lepidomysidae (A, B, FH, K, M) and Stygiomysidae (C-E, J, L, N). A, antennula of male Spelaeomysis cardisomae
Bowman, 1973; B, antenna of the same male as in (A); C, antennula of female Stygiomysis
aemete Wagner, 1992; D, antenna of the same female as in (C); E, right mandible of the same
female as in (C); F, left mandible with labrum in situ, Spelaeomysis cardisomae; G, masticatory
portion of the left mandible in Spelaeomysis bottazzii Caroli, 1924; H, maxillula in Spelaeomysis
longipes (Pillai & Mariamma, 1964); J, maxillula in Stygiomysis hydruntina (Pillai & Mariamma,
1964); K, maxilla in Spelaeomysis cochinensis Panampunnayil & Viswakumar, 1991; L, maxilla in
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small terminal segment separated by a transverse or oblique articulation. Its borders are
mostly lined by plumose setae; nonetheless, the outer border may be (in part) smooth,
serrated, or spinose. The outer border is slightly dimorphic in Eucopia australis. In the
lophogastrid Ceratolepis hamata the antennal scale is curiously modified, resembling a
fishhook (fig. 54.10F). Within the Stygiomysida it is small in Spelaeomysis (figs. 54.7J,
54.11B) and only vestigial (fig. 54.11D) in Stygiomysis. It is vestigial also in a few
Mysida, for example miniaturized and scale-like in Palaumysis, reduced to a small spine
in Arachnomysis and Chunomysis, and small, styliform in Caesaromysis (fig. 54.12C).
Mouthfield (figs. 54.13A, 54.14A). – The mouth is delimited anteriorly by the unpaired labrum, posteriorly by the paired lobes of the labium, and laterally by three pairs
of appendages, i.e., the mandibles, maxillules, and maxillae. More caudally, the area of
the mouthparts in Mysida is closed by an anteriorly directed lobe (fig. 54.15M) originating from the first thoracic sternite. De Jong-Moreau et al. (2001) found that gut content
analyses generally agreed well with the morphology of peri-oral structures in Mysidae species, reflecting the different feeding types: saprophagous (Bacescomysis abyssalis),
phytophagous (Birsteiniamysis inermis), omnivorous (Hemimysis speluncola), and carnivorous (Siriella armata). Remarkably, their results suggest that a large processus molaris
is not always associated with herbivorous feeding as was previously generally assumed
(Mauchline, 1980).
Labrum (figs. 54.10H, 54.11F, 54.13B, F, 54.14A, C, 54.15A-C). – The labrum
has the form of a ventrally protruding hump, anteriorly mostly rounded and posteriorly
truncate. However, in the Siriellinae, Gastrosaccinae, Mysidellinae, and certain Mysinae
it extends anteriorly in a median spiniform process (fig. 54.15C). The posterior margin
is formed by two asymmetrical lobes bearing setae, small spines, cuticular ridges,
and/or tooth-like structures. In the Lophogastridae, Gnathophausiidae, Boreomysinae, and
certain Erythropinae, the right lobe forms a kind of inwards-bent tooth. In Gnathophausia
longispina this tooth bears stiff setae that appear apically frayed (fig. 54.13B). As a
diagnostic character of the Mysidellinae, the ventral face of the labrum is posteriorly
produced into two strongly unequal lobes. In Lophogaster typicus, the external face of
the labrum is occupied by numerous pores associated with glandular units involved in
coating and digesting food; accordingly, the labrum plays a role not only in the mechanical
but also in the chemical breakdown of food (De Jong et al., 2002).
Mandible (figs. 54.10H, J, 54.11E-G, 54.13A, E, 54.14, 54.15D). – The asymmetric
mandibles are composed of a trunk and a three-segmented palp, whereby the proximal
segment is the shortest. The inner margin of the trunk shows four domains, presented here
in a series from distal to proximal (fig. 54.14C): the pars incisiva (processus incisivus)
Stygiomysis aemete; M, labium (paragnaths) in Spelaeomysis longipes; N, left paragnath in Stygiomysis aemete. Abbreviations: af, antennal flagellum; as, antennal scale; ba, basis; cx, coxa; ed, endite;
pl, palp. [A, B, F, after Bowman, 1973; C-E, L, N, after Wagner, 1992; G, after Ariani, 1982; H, M,
after Pillai & Mariamma, 1964; J, after Gordon, 1960; K, after Panampunnayil & Viswakumar,
1991; E, K, N, modified.]
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Fig. 54.12. Antennae in the Mysida families Petalophthalmidae (A, B) and Mysidae (C-L). A,
eyeplate and left antennula and antenna of female Hansenomysis pseudofyllae Lagardère, 1983,
dorsal; B, cephalic region of female Petalophthalmus armiger Willemoës-Suhm, 1875, lateral; C,
cephalic region of male Caesaromysis hispida Ortmann, 1893, dorsal; D, cephalic region of female
219
and the digitus mobilis (lacinia), each with several strong, mostly smooth teeth; the pars
centralis (processus incisivus accessorius, spine row) usually with serrated or spinose
teeth; and the pars molaris (processus molaris) with a more or less strong grinding surface.
The equipment of the domains with teeth or grinding lamellae varies between the left and
right mandibles. Size and strength of the partes molares vary with the feeding habits of
the various species (Mauchline, 1980). Certain domains may be missing in some genera.
Particularly, the right digitus mobilis is often rudimentary or missing. The inner margin of
the trunk is rectilinear and forms a broad cutting blade in Mysidella. The mandibular palp
commonly shows moderate variations. In several species of Petalophthalmus, however, it
is strongly enlarged and prehensile with a serrated inner margin of the median segment
(fig. 54.12B). In Lophogastrida, the right mandible shows no digitus mobilis (lacinia;
Richter, 2003), and the left mandible bears a semicircular incisory process and a furrow
that receives the strongly developed left paragnath of the labium. According to B. Casanova
et al. (2002) the gnathal part of the mandibles is prolonged by portions of the pleurites and
tergites of the mandibular somite during larval development in Lophogastrida, Mysida,
Euphausiacea, and certain Decapoda.
Labium (figs. 54.10K, 54.11M, N, 54.13C, D, 54.14A, 54.15H). – The labium of
the Mysidae is generally formed by two roughly symmetrical paragnaths that are
more or less connected at their base. The labium of Thalassomysis is aberrant by the
strongly asymmetrical paragnaths showing a very large common basis; and by the right
paragnath showing a cavity to receive part of the labrum. In the Stygiomysida genus
Stygiomysis the paragnaths are long (fig. 54.11N) and apically widely separated. The left
paragnath is more strongly developed than the right (fig. 54.10K) in most, probably all,
Lophogastrida (Clarke, 1961b; Richter, 2003). Its anterior and inner faces are lined by
tubercles and ridges, forming a masticatory structure together with the concave posterior
margin of the corresponding mandible (Clarke, 1961b). The well-studied paragnaths of
Gnathophausia childressi (fig. 54.13C, D) show a strong musculature comparable to that
of the maxillipeds. They possibly actively contribute to mastication, like the mandibles
with which they are connected. The presence of molar structures on the left paragnath
(fig. 54.10K), stronger than on the right one, supports this hypothesis (J.-P. Casanova,
1996b).
Diamysis lagunaris Ariani & Wittmann, 2000, dorsal; E, antennula of male Diamysis fluviatilis
Wittmann & Ariani, 2012, dorsal; F, antennula in female Diamysis fluviatilis; G, antennula of male
Anchialina truncata (G. O. Sars, 1883), ventral; H, antenna of male Anchialina truncata, dorsal;
J, antenna of Siriella castellabatensis Ariani & Spagnuolo, 1976; K, antennal scale of Praunus
flexuosus (O. F. Müller, 1776); L, antenna of Diamysis mesohalobia Ariani & Wittmann, 2000.
Abbreviations: apm, appendix masculina; cal, callynophore; fp, fenestra paracornealis; plm, palpus
mandibularis; sa, sacculus (end sac) of the antennal gland. [A, after Lagardère, 1983; B, after
Tattersall & Tattersall, 1951; C, after O. S. Tattersall, 1955; D, L, after Ariani & Wittmann, 2000;
E, F, after Wittmann & Ariani, 2012b; G, H, after G. O. Sars, 1885a; J, after Ariani & Spagnuolo,
1976; K, after G. O. Sars, 1879; A, B, D-L, modified.]
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Fig. 54.13. Structures of the mouthfield in the Lophogastrida species Gnathophausia longispina
G. O. Sars, 1883 (A-E) and Gnathophausia childressi Casanova, 1996 (F). A, mouth area in ventral
view; B, detail of labrum; C, D, inner lateral view on medio-sagittal sections of mouth area, showing
coaptation of the right (C) and left (D) paragnaths; E, F, details of grinding surfaces of mandibles (E)
and labrum (F). Abbreviations: l, labrum; m, mandibles; p, paragnaths. [A, C-F, after J.-P. Casanova,
1996b; B; after Nouvel et al., 1999.]
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Fig. 54.14. Structures of the mouthfield in Mysidae (Mysida). A, Birsteiniamysis inermis
(Willemoës-Suhm, 1874), mouthparts sensu stricto in ventral view; B, Neomysis rayii (Murdoch,
1885), musculature of right mandible in inner lateral view; C, Hemimysis lamornae (Couch, 1856),
details of labrum and masticatory edges in ventral view. Abbreviations: lb, labrum; lm, lacinia mobilis; mda, mdp and mv, dorsal-anterior (mda), dorsal-posterior (mdp), and ventral (mv) muscles, respectively; pa, paragnaths (labium); pce, pars centralis (processus incisivus accessorius, spine row);
pic, pars incisiva (processus incisivus); plm, palpus mandibularis; pm, pars molaris (processus molaris); trm, mandibular trunk (endite). [A, after G. O. Sars, 1885b; B, after Snodgrass, 1952; C,
modified after Cannon & Manton, 1927a.]
Maxillula (figs. 54.10L, M, 54.11H, J, 54.15E). – According to the interpretation by
Hansen (1925) the maxillula is formed by three segments (praecoxa, coxa, basis) of the
sympod. Coxa and basis each bear an endite with setae and spines. The Gnathophausiidae
(fig. 54.10M) and the Lepidomysidae (fig. 54.11H) each show a small, two-segmented,
retroverted palp that may be interpreted as a vestigial endopod. In the Mysidae and
certain Gnathophausiidae, there is a small lamelliform, setose lobe (pseudoexopodite;
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Fig. 54.15. Mouthparts and maxillipeds in the Mysida families Petalophthalmidae (A, F, J, K, O)
and Mysidae (B-E, G, H, L-N). A, labrum of Hansenomysis atlantica Lagardère, 1983, ventral;
B, labrum of Heteromysis arianii Wittmann, 2000, oblique ventral view; C, labrum of Gastrosaccus roscoffensis Băcescu, 1970, slightly oblique ventral view; D, mandibles of Heteromysis
arianii, caudal aspect; E, maxillula of Heteromysis arianii, caudal; F, maxilla of Hansenomysis
atlantica, caudal; G, maxilla of Heteromysis arianii, frontal aspect; H, labium (paragnaths) of
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fig. 54.15E), folded from the base, considered by Hansen (1925) to be an exite of the
praecoxa.
Maxilla (figs. 54.10N, O, 54.11K, L, 54.15F, G). – The second maxilla resembles a
series of leaves with a common basis. It shows a quite uniform structure with the sympod
consisting of three more or less distinct segments: the coxa with a simple endite, and the
basis with a bilobate endite. These endites bear dense rows of mostly plumose setae along
their margins. The endopod (= maxillary palp) is reduced to two foliaceous segments;
the terminal margin of its distal segment is well equipped with setae. In addition, it
is armed with spines or teeth in various taxa. The exopod is usually represented by a
rounded plate with setae along the outer margin. However, it is reduced or completely
absent (Metamysidopsis) in a few species. On the outer margin of the coxa of the
Gnathophausiidae, a red papilla (fig. 54.10O) marks the common orifice of two glands
producing a luminescent secretion.
Thoracic appendages
General structure of the thoracopods (figs. 54.16, 54.17A-F, 54.18). – All taxa have
eight pairs of thoracic appendages. The anterior two pairs of endopods are normally modified as maxillipeds (fig. 54.15M, N). Only the Eucopiidae (fig. 54.19A, B) and the Stygiomysidae (fig. 54.17D) show four pairs of maxillipeds. It is a matter of definition whether
the prehensile third endopods, termed gnathopods (fig. 54.18H), of many Heteromysinae
(Mysidae) are to be counted as maxillipeds.
The thoracopods were classically described as consisting of a one-segmented sympod
with an endopod and a natatory exopod. The endopod was schematized as five main
articles: a short ischium, elongate merus and carpus, elongate propodus (often secondarily
subdivided), and a short dactylus with claw. The main knee was seen between carpus and
propodus (Băcescu, 1954). The exopod appears composed of a basal plate and a multiarticulate flagellum bearing plumose setae.
Based on the comparative anatomy of the Malacostraca and on the study of the
musculature (principally the flexor and extensor dactyli), Hansen (1925) proposed a
modified concept for the mysidaceans (fig. 54.18A-G): firstly, the sympod shows a more
or less distinct subdivision in basis and coxa, sometimes also a praecoxa. Secondly,
the main articulation of the leg is placed between merus and carpus. Proximally to
Heteromysis arianii; J, first thoracic endopod (maxilliped 1) of Petalophthalmus armiger WillemoësSuhm, 1875, caudal; K, first thoracic endopod with epipod in Hansenomysis atlantica, caudal; L,
first thoracic endopod of Mysidopsis gibbosa G. O. Sars, 1864; M, first thoracopod (caudal aspect)
with thoracic sternites 1-6 (ventral) in female Heteromysis arianii; N, second thoracic endopod
(caudal) with thoracic sternites 1-8 (ventral) in male Heteromysis arianii; O, second thoracopod of
Hansenomysis pseudofyllae Lagardère, 1983, caudal. Abbreviations: ba, basis; cr, carpus; cx, coxa;
da, dactylus; is, ischium; mis, merischium; pr, propodus; ps, pseudexopodite; sp1, sp3, sp7, processes
from sternites 1, 3, or 7; ts1, ts6, ts8, thoracic sternites 1, 6, and 8, respectively. [A, F, K, O, after
Lagardère, 1983; B, D, E, G, H, M, N, after Wittmann, 2000; C, after Wittmann et al., 2011; J, L,
after Tattersall & Tattersall, 1951; A, E, G, J-L, O, modified.]
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Fig. 54.16. Thoracopods and pleopods in the Lophogastrida families Eucopiidae (A, E, F, H, J)
and Gnathophausiidae (B-D, G, K, L). A, first thoracopod of Eucopia australis Dana, 1852; B,
the same for Gnathophausia longispina G. O. Sars, 1883; C, second thoracopod of Gnathophausia
longispina; D, third thoracopod of male in Gnathophausia longispina, branchiae removed to render
rudimentary epipod (rep) visible; E, fifth thoracopod in Eucopia australis; F, terminal portion of
endopod as in (E); G, eighth thoracopod with male gonopore (g) in Gnathophausia longispina; H,
pleopod of Eucopia australis female; J, pleopod of Eucopia australis male; K, second male pleopod
in Gnathophausia zoea Willemoës-Suhm, 1873; L, terminal portion of endopod as in (K). [A-J,
modified after G. O. Sars, 1885a; K, L, after Lagardère & Nouvel, 1980a; K, modified.]
this articulation there are three articles: praeischium, ischium, and merus. Distally there
are as a general rule (e.g., in Siriella; fig. 54.18B) the carpus, the propodus, and the
dactylus with claw. In many Erythropinae the carpus is separated from the (one- to
multi-segmented) propodus by an oblique segmental border (fig. 54.18D). Depending on
225
genera and higher taxa, the carpus and the propodus may be distinct, or may be fused to
form a carpopropodus (fig. 54.18F, G), which, then, may be subdivided by secondary
articulations. In case of only one subdivision, its significance may be established based on
the course and insertion of the musculature. This scheme was adopted by most subsequent
authors (e.g., Tattersall & Tattersall, 1951). Nonetheless, the concept of a fused and then
subdivided carpopropodus should not be used in an over-schematized manner. There is a
great diversity between taxa, particularly within the order Mysida. In many Mysinae and
Leptomysinae, particularly in Paramysis (fig. 54.19E), the first segment after the knee may
be identified as carpus due to different size, development, and setation patterns compared
to the remaining propodal segments.
First thoracopod (figs. 54.15M, 54.16A, B, 54.17A, B). – The endopod is pediform
only in the Carboniferous Lophogastrida Peachocarididae (Schram, 1986). In extant taxa
it is modified as a maxilliped throughout. It is more or less shortened, sturdy, compressed,
formed by 5-7 articles and a terminal claw. The two distal articles are broadened and
flattened. They are turned to the sagittal plane of the body, thus forming with the endites
of the proximal articles a scissor-like structure. In certain species of Boreomysis the distal
article forms a subchela together with a bulge of the preceding article. Well-developed
endites may be present on 1-4 basal articles of the endopod. Occasionally, some of the
basal articles may be fused. The basis may show a great transversal extension due to a
large distance between exopod and endopod. In most taxa the sympod bears a foliaceous
epipod penetrating into the carapace cavity. Most Mysida show a typically small endite
inserting subterminally on the inner anterior face of the basis (fig. 54.15M). In this order,
the exopod is generally well developed, with basal plate and a mostly eight-segmented
flagellum (fig. 54.15M): in Mysimenzies (Mysida: Erythropinae) the exopod is reduced to
a lamina, in the Lophogastrida to an unsegmented blade (fig. 54.16A) or rod (or may be
vestigial; fig. 54.16B), in the Stygiomysida to a leaf-like blade (fig. 54.17A, B). The first
exopod is completely reduced in the Petalophthalmidae (Mysida).
Second thoracopod (figs. 54.15N, 54.16C). – The endopod normally shows less
strong modifications as a maxilliped compared to that of the first thoracopod. Shape
and degree of modification vary according to the various taxa. At family level, this
endopod is least maxilliped-like, more closely resembling the subsequent thoracopods
in the Gnathophausiidae (fig. 54.16C). Basal endites are present in several taxa, e.g.,
Ceratomysis. The distal article of the endopod is often flat, with brushes of setae and
spines. The second endopod may show a prehensile structure interpreted as suitable for
grasping or for brushing. In the Stygiomysida it is prehensile. The second exopod is well
developed, natatory in this order, as in the Lophogastrida, and in most Mysida, but missing
in Hansenomysinae (Mysida: Petalophthalmidae).
Third to eighth thoracopods (figs. 54.16D-G, 54.17C-F, 54.18, 54.19B, E). – These
appendages are almost always well developed. The natatory exopods consist of a basal
plate and a multi-segmented, setose flagellum. Differences at specific level concern
mainly segmental numbers of the flagellum and the outer corner (rounded or spiniform) of
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Fig. 54.17. Thoracopods, pleopods, and pleon in the Stygiomysida families Lepidomysidae (A, C, F,
G, K, M) and Stygiomysidae (B, D, E, H, J, L). A, first thoracopod in Spelaeomysis olivae Bowman,
1973; B, first thoracopod in Stygiomysis holthuisi (Gordon, 1958); C, third thoracic endopod in
Spelaeomysis longipes (Pillai & Mariamma, 1964); D, fourth thoracopod in Stygiomysis aemete
227
the basal plate of the exopods (Ariani & Wittmann, 2000). As an exception, exopod 8 is
missing in the lophogastrid Ceratolepis hamata.
The endopods are typically pediform. Their length may be subequal to conspicuously
unequal. In Mysidae, the length typically increases from endopod 3 caudally up to
endopod 6 or 7, and may decrease behind. The third and fourth endopods are modified
as maxillipeds (gnathopods) in the Eucopiidae (fig. 54.19B) and the Stygiomysidae (fig.
54.17D), similarly the third but not the fourth in Lepidomysidae (fig. 54.17C). In certain
Heteromysinae (Mysidae) the third endopods are considered to be gnathopods, because
they are more robust than the posterior endopods and because their strong claw folds up
to act as a prehensile subchela (fig. 54.18H). The eighth endopods are rudimentary in
Rhopalophthalmus and even more strongly reduced in Pseudomysidetes. In contrast, they
are strong and prehensile in Hyperiimysis. The Eucopiidae show a very particular structure
of the thoracopods (fig. 54.2D): endopods 2-4 are short but strong and subchelate (fig.
54.19A, B), endopods 5-7 are very long, thin and subchelate (fig. 54.16E, F), whereby
endopod 8 is almost normal and slender but without claw.
Important variations regard numbers and structure of the distal, i.e., the ‘tarsal’, articles
of the endopods: carpus and propodus distinct or fused to a carpopropodus or, in turn,
the carpopropodus subdivided into a few up to many articles (fig. 54.18B-G; cf. above). In
the Mysida genus Diamysis, the numbers of carpopropodal segments in the series of third
to eight thoracic endopods show some variability (2-3, exceptionally 3-4); nonetheless,
the patterns of segment numbers are within certain limits characteristic of different
(sub)species. The dactylus of the Mysida may be normal (fig. 54.18H-M) or more or
less distinctly fused with the claw, or may be rudimentary, as in the last thoracopod of
Paramysis pontica. In certain cases there is no claw. In addition to the normally present
claw, the dactylus may bear several setae (fig. 54.18K, O). Those below the claw are
termed subungulary setae (fig. 54.18O); they may be long, occasionally microserrated,
and may resemble a second claw, particularly if the true claw is thin, needle- or setalike. On the terminal margin of the propodus there are often 1-2 (mainly two) pairs of
paradactylary setae (fig. 54.18O) flanking the dactylus. Some of these setae are often
microserrated and/or may show series of thin secondary projections together forming
comb-like structures. Some of the latter have been interpreted as cleaning setae (see below,
‘Grooming’).
Branchiae (figs. 54.6E, 54.16C, E, G, 54.19B). – Arborescent gills at the coxae of
thoracopods are typical of the order Lophogastrida. Hansen (1925) and Tattersall &
Wagner, 1992; E, eighth thoracopod in Stygiomysis aemete; F, eighth thoracopod in male Spelaeomysis olivae; G, second pleopod in male Spelaeomysis olivae; H, second pleopod in male Stygiomysis
holthuisi; J, second pleopod in female Stygiomysis holthuisi; K, third pleopod in male Spelaeomysis
cardisomae Bowman, 1973; L, pleon of female Stygiomysis holthuisi in lateral view; M, pleomeres
3-5 in male Spelaeomysis cardisomae, ventral. Abbreviations: ba, basis of sympod; cl, coxal lobe;
end, endopod; ep, epipod; ex, exopod; sl3 to sl5, sternal lamellae from pleomeres 3-5. [A, F, G, K,
M, after Bowman, 1973; B, H, J, L, after Gordon, 1960; C, after Pillai & Mariamma, 1964; D, E,
after Wagner, 1992; D, E, G, modified.]
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Fig. 54.18. Structure of the thoracopods 3-8 in the Mysida families Mysidae (A-K, M, O) and
Petalophthalmidae (L, N). A-G, endopod structure according to interpretation of Hansen (1925, setae
partly omitted). A, Praunus Leach, 1814, lateral view on thorax showing bases of endopods 2-5; BG, distal portions of posterior endopod in Siriella Dana, 1850 (B), Boreomysis G. O. Sars, 1869 (C),
229
Tattersall (1951) interpreted these branchiae as epipods (quoted by them as pre-epipods),
i.e., as podobranchiae. If any, there are normally four gills per thoracopod. The main gill
is often directed medially and may surround the leg from behind to meet the remaining
three gills that are arranged laterally below the lateral projection of the carapace. The
lophogastrid gills are always found on thoracopods 3-7, and are generally more strongly
developed in males than in females. There is an additional rudimentary gill on thoracopod
8 in Gnathophausia (fig. 54.16G). Eucopia crassicornis from oxygen-poor waters in
the Canal of Mozambique shows more strongly developed branchiae compared with the
congeneric species from waters with normal oxygen levels (J.-P. Casanova, 1997). There
are no branchiae in the Stygiomysida and Mysida; however, small humps with thin cuticle
in comparable position may possibly represent rudiments of branchiae in a few forms of
the latter order.
Oostegites (fig. 54.19). – The brood lamellae are attached at the basis of the inner (= medial) margins of the thoracic appendages, together forming a brood pouch
(marsupium) in females. The Lophogastrida, one family (Lepidomysidae) of the Stygiomysida, and the more primitive (sub)families of the Mysida show a total of seven pairs
of oostegites on thoracopods 2-8 (fig. 54.19A, D). The Stygiomysidae, as the second family
of Stygiomysida, have only four pairs of oostegites in unique position at thoracopods 4-7
(Bowman et al., 1984). Within the order Mysida the numbers of oostegites show a clear
tendency for reduction: seven pairs in Petalophthalmidae and Boreomysinae, four pairs in
Thalassomysis, and only 1-3 pairs (or 2-4, including vestigial ones) in the remaining taxa.
In Mysida, the oostegites arise from the posterior thoracopods and are largest on thoracopod 8. Fully developed oostegites bear rows of plumose setae at least along the lower
margins. Not considering these setae, the oostegites may represent simple plates or may be
equipped with motile or immotile ventilation (fig. 54.19E) or cleaning lobes. These lobes
are furnished with long, microserrated or barbed setae. Functionally similar lobes may also
arise from thoracic sternites (fig. 54.19F, G). In certain taxa of Mysida, unpaired foliaceous
sternal lobes from the eighth thoracomere (fig. 54.19G), or paired pleural plates from the
first pleomere (fig. 54.5F), may contribute to the posterior closure of the marsupium.
Amblyops G. O. Sars, 1872 (D), Anchialina Norman & Scott, 1906 (E, endopod 5), Mysidopsis G. O.
Sars, 1864 (F), and Praunus (G); H, third thoracopod in female Heteromysis dardani Wittmann,
2008; J, ‘tarsus’ of third endopod in Diamysis camassai Ariani & Wittmann, 2002; K, ‘tarsus’ of
fourth endopod in Ischiomysis telmatactiphila Wittmann, 2013; L, fifth endopod with oostegite in
adult female Hansenomysis nouveli Lagardère, 1983; M, sixth endopod with rudimentary oostegite
in adult female Diamysis camassai, arrows indicate mode of measurement of merus length and
width; N, sixth thoracopod in Hansenomysis abyssalis Lagardère, 1983, setae of exopod omitted; O,
tip of eighth thoracic endopod in male Diamysis mesohalobia Ariani & Wittmann, 2000; P, eighth
thoracopod with penis in Heteromysis wirtzi, terminal portion of exopod omitted. Abbreviations: ba,
basis; cr, carpus; cx, coxa; da, dactylus; ex, exopod; is, ischium; me, merus; pas, paradactylary setae;
pcx, praecoxa; pe, penis; pi, praeischium; pr, propodus; sus, subungulary seta; te, tergite; ug, unguis.
[A-G, after Hansen, 1925, as arranged by Nouvel et al., 1999, again modified; H, P, after Wittmann,
2008; J, M, after Ariani & Wittmann, 2002; K, after Wittmann, 2013a; L, N, after Lagardère, 1983;
O, after Ariani & Wittmann, 2000; A-G, K, L, N-P, modified.]
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Fig. 54.19. Oostegites and associated structures in the Lophogastrida (A, B), Stygiomysida (C, D)
and Mysida (E-L). A, Eucopia australis Dana, 1852, lateral, distal portions of thoracic endopods
5-8 omitted; B, same species, third thoracic endopod with gills and oostegite, lateral; C, Spelaeomysis bottazzii Caroli, 1924, incubating 4 eggs, in vivo, ventral; D, same species, living specimen
231
In addition, many species show hairy lamellae or ventilation plates on the bases
of oostegite-bearing thoracopods, suggesting that these structures represent rudimentary
(parts of) oostegites. The oostegites are generally reduced during the repose of the ovaries
in Lophogastrida (J.-P. Casanova, 1977) and Stygiomysida (Ariani & Wittmann, 2010), as
is the case in most remaining orders of Peracarida. A reduction of the oostegites at the end
of the reproductive period was reported by Nouvel & Nouvel (1939) for the mysid Praunus
flexuosus from north-eastern Atlantic coasts. Nonetheless, in most Mysida the oostegites
are generally not reduced at the moult after release of the young (Ariani & Wittmann,
2000).
External male genitalia (figs. 54.4L, 54.16G, 54.18P, 54.20). – In the males of Mysida,
with the exception of the Rhopalophthalminae, there is a well-developed tubular penis
(fig. 54.20C, E-G) arising from the coxa of each eighth thoracopod. The gonopore is
(sub)terminal in posterior position. It is typically flanked by two or more setose lobes
forming a closing apparatus (valves; fig. 54.20C, D, G). The penes may be very large
in several genera (Mysidetes, Pseudomysidetes, Mysidella; Lagardère & Nouvel, 1980b;
Wittmann, 2013b). In certain taxa, the normally slightly bent, subcylindrical penes can
be enlarged by large terminal lobes (Ischiomysis in fig. 54.20G, certain Heteromysis;
Wittmann, 2013a) or by longitudinal wing-like blades (Paramysis; Daneliya et al., 2007;
Wittmann & Ariani, 2011). The penes of Mysifaun erigens may be expanded to giant
size by erectile tissue (fig. 54.20E; Wittmann, 1996). A strange situation was found
by Wittmann (2013b) in two species of Rhopalophthalmus (Rhopalophthalminae; fig.
54.20D): there is no penis, but the genital opening is flanked by two small lobes distally on
the inner margin of the strongly enlarged coxa of the eighth thoracopods. The vas deferens
is terminally widened in a large seminal vesicle occupying most of the space within this
coxa. Endopod 8 is vestigial in males, more strongly reduced compared to the also reduced
endopod in females. Only the males bear a rounded pleural plate (arrow in fig. 54.4C)
ventrally projecting from the first pleomere, and show modified second pleopods (fig.
54.21C). The close spatial vicinity of these uncommon structures suggests some role in
the unknown process of mating in this subfamily.
Both genera (families) of Stygiomysida have no penes. The male gonopore is between
an anterior setose and a posterior bare lobe on the inner margin of the (not conspicuously
enlarged) coxa of the eighth thoracopods. These lobes are of about equal size (fig. 54.20B)
demonstrating its individual oostegites by keeping them straddled, lateral; E, eighth thoracopod
of Paramysis pontica Băcescu, 1940, note setose ventilation lobe (vl) caudally on oostegite; F,
‘ventilation lobes’ of fourth thoracic sternites in Gastrosaccus widhalmi (Czerniavsky, 1882); G,
special processes from thoracic sternites 7 and 8, probably involved in incubating the young of
Neomysis integer (Leach, 1814), lateral; H-K, series of oostegites 1-3 in Leptomysis lingvura marioni
Gourret, 1888, inner lateral view; L, right half of brood pouch in Diamysis camassai Ariani &
Wittmann, 2002, inner lateral view, part of appendages and setae omitted. Abbreviations: co7, co8,
‘cotyledons’ from seventh and eighth sternites, respectively; ga, grooming appendage; mp, median
sternal plate; vl, ventilation lobe. [A, B, after G. O. Sars, 1885a; C, D, photo Antonio P. Ariani, part
of background cleaned with electronic tools; E, after Băcescu, 1954; F, after Băcescu, 1940; G, after
Nouvel et al., 1999; H-K, after Wittmann, 1982; L, after Ariani & Wittmann, 2002; B, E, F, H-K,
modified.]
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Fig. 54.20. External male genitalia as derivates of the eighth thoracopods in the Lophogastrida (A),
Stygiomysida (B), and Mysida (C-G). A, Eucopia unguiculata (Willemoës-Suhm, 1875); B, Stygiomysis hydruntina Caroli, 1937; C, Pseudomma armatum Hansen, 1913; D, Rhopalophthalmus
terranatalis O. S. Tattersall, 1957; E, Mysifaun erigens Wittmann, 1996; F, Heteromysis armoricana
H. Nouvel, 1940 (setae partly omitted); G, Ischiomysis telmatactiphila Wittmann, 2013. Abbreviations: ba, basis; cx, coxa; de, ductus ejaculatorius; end, (insertion of) endopod; ex, (insertion of)
exopod; g, gonopore; pe, penis; sp7, sp8, processes from sternites 7 and 8; sv, seminal vesicle. [A-D,
after Wittmann, 2013b; E, after Wittmann, 1996; F, after Nouvel, 1940 (scale corrected); G, after
Wittmann, 2013a; A-G, modified.]
in Stygiomysis, whereas the anterior lobe (fig. 54.17F) is distinctly larger than the posterior
one in Spelaeomysis. Also this pair of lobes forms a closing apparatus (valve) similar to
the more diverse lobes on the penis in Mysida. The Lophogastrida males show only a
slot-like orifice, without lobes, on the coxae of the eighth thoracopods (fig. 54.20A). The
gonopore is on top of an anvil-like elevation in Paralophogaster, or of a dome-shaped
elevation in Gnathophausia. There is no distinct elevation in two species of Eucopia and
one Lophogaster examined by Wittmann (2013b).
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Pleonal appendages
P LEOPODS
A pair of pleopods inserts latero-ventrally on each of the first to fifth somites of the
pleon. The pleopods represent uniramous or biramous, more or less natatory to reduced,
rod-like appendages, showing consistent differences between the various taxa from order
down to genus level.
Lophogastrida (fig. 54.16H-L). – The lophogastrids have a large, flat shaft (sympod)
formed by a short coxa and a much longer basis, the latter bearing two natatory, multisegmented rami furnished with plumose setae. The sexual differentiations of the male
pleopods are weak. This regards modifications of the second endopod (fig. 54.16K, L)
in Gnathophausiidae (Lagardère & Nouvel, 1980a), and an average larger size of male
pleopods (fig. 54.16J) compared to that in females (fig. 54.16H) in Eucopiidae (Tattersall
& Tattersall, 1951).
Stygiomysida (fig. 54.17G-L). – All pleopods are biramous, but are nonetheless reduced in both sexes. The reduction regards the number of segments: sympod and endopod
each are unsegmented, and the exopod reduced to a few segments. The exopod of the
second male pleopod is slightly modified and has only two segments in Stygiomysis hydruntina (fig. 54.17H) or three in Spelaeomysis bottazzii (fig. 54.17G). In females of both
species, the same exopod shows one additional articulation compared to the respective
males.
Mysida (fig. 54.21). – The pleopods are more or less rudimentary, rod- or plateletlike in females (but biramous in females of Archaeomysis). The pleopods of males are
typically less reduced, but there is at least some reduction in the endopod of the first pair.
Several subfamilies of the Mysidae have one, rarely more, modified male pleopods, which
may play some role in mating (probably not directly involved in sperm transfer). With
some variations according to the genera, the male modifications regard mainly the second
exopod in Rhopalophthalminae (fig. 54.21C), the third in Gastrosaccinae (fig. 54.21KM), and the fourth in Mysinae (fig. 54.21O-Q) and Leptomysinae (fig. 54.21N). In certain
genera of Gastrosaccinae the third male pleopods show very complex modifications (fig.
54.21K, L). In males of most Siriellinae the endopods of pleopods 2-5 have spirally coiled
exites (= pseudobranchial lobes; fig. 54.21G). In many species of Siriellinae modified
setae are present on both rami of the fourth pair of male pleopods, occasionally also on the
third pair, exceptionally on the endopod of the second pair. In the Erythropinae, the male
pleopods are mostly not or only weakly modified, rarely with a strongly modified seta as
in Parapseudomma calloplura (fig. 54.21J); if any modification, then mostly regarding one
or more of endopods 2-5, or again less frequently of exopods 2-5 (Nouvel & Lagardère,
1976). In males of certain Boreomysinae, there are small modifications of the third exopod
(fig. 54.21D), rarely of the second plus third exopods. In Mysidellinae, Heteromysinae
(except Harmelinella), and Palaumysinae, all pleopods are rudimentary in both sexes,
although several taxa show some small modifications exclusive of males (fig. 54.21R-U).
234
235
In Palaumysis the fourth pleopod bears a large apical, spine-like modified seta in males
only (fig. 54.21U; Hanamura & Kase, 2003). The males of several species (subgenera)
of Heteromysis are characterized by modified setae and/or spines on some of pleopods
2-5 (Wittmann, 2008; Price & Heard, 2011). In contrast to the remaining Heteromysinae,
the males of Harmelinella show a uniramous and sub-segmented third pleopod, which is
elongate and apically modified (Ledoyer, 1989).
U ROPODS
The paired uropods insert latero-terminally on the sixth pleonite (figs. 54.1C, D,
54.2C, 54.3A, 54.19C, 54.22A-D, F-N). They consist of a short unsegmented sympod
bearing two dorso-ventrally flattened rami, together with the unpaired telson constituting
the usually strong tail fan. Considered an exclusive feature among the three orders, the
sympod of the Stygiomysida shows a spinose, backwards-directed inner lobe. In the
family Stygiomysidae this lobe is strong, reaching nearly to the tip of both rami of the
uropod; its set of large spines extends even further (fig. 54.22F). A distinct, but much
shorter spinose lobe is present in the Lepidomysidae (fig. 54.22G, H). The exopod is
subdivided in its distal half by a transverse suture in certain Lophogastrida (Eucopiidae
and Gnathophausiidae; fig. 54.22C, D) and Stygiomysida (Lepidomysidae; fig. 54.22G,
H). Within the Mysida it is subdivided in the Petalophthalmidae (fig. 54.22J) and two
subfamilies of the Mysidae: the Siriellinae and Rhopalophthalminae (fig. 54.22K, L).
There is an incomplete, subbasal suture in Boreomysinae. The exopod is undivided in the
Fig. 54.21. Pleopods in the Mysida families Petalophthalmidae (A, B) and Mysidae (C-U), the latter
represented by all ten of its acknowledged subfamilies: Rhopalophthalminae (C), Boreomysinae (D),
Siriellinae (E-H), Erythropinae (J), Gastrosaccinae (K-M), Leptomysinae (N), Mysinae (O-Q), Heteromysinae (R, S), Mysidellinae (T), and Palaumysinae (U). A, fifth pleopod of male Hansenomysis
abyssalis Lagardère, 1983, setae in part truncated; B, the same for female Hansenomysis nouveli
Lagardère, 1983; C, second male pleopod in Rhopalophthalmus egregius Hansen, 1910; D, third
male pleopod in Boreomysis megalops G. O. Sars, 1872; E-H, Siriella clausii G. O. Sars, 1877, first
pleopods of male (E) and female (F), second pleopod of male (G), and fifth pleopod of female (H); J,
fourth male pleopod in Parapseudomma calloplura (Holt & Tattersall, 1905); K, strongly modified
terminal portion of exopod of third pleopod in terminal male of Coifmanniella johnsoni (W. M. Tattersall, 1937); L, third pleopod of subterminal male of Chlamydopleon aculeatum Ortmann, 1893;
M-Q, fourth male pleopods in Paranchialina angusta (G. O. Sars, 1883) (M), Leptomysis heterophila
Wittmann, 1986 (N), Diamysis cymodoceae Wittmann & Ariani, 2012 (O), Limnomysis benedeni Czerniavsky, 1882 (P), and Mysis mixta Lilljeborg, 1852 (Q), respectively; R, S, first (R) and second (S)
male pleopods of Heteromysis wirtzi Wittmann, 2008; T, first male pleopod in Mysidella biscayensis
Lagardère & Nouvel, 1980; U, third male pleopod in Palaumysis pilifera Hanamura & Kase, 2003.
Abbreviations: acl, accessory lobe; ap, apophysis; asp, apical spine; bl, blade; bo, bow; dl, distal
lobe; end, endopod; ex, exopod; ib, inner branch; ist, inner stylet; obr, outer branch; ost, outer stylet;
psl, pseudobranchial lobe (exite); sap, subapical spine; sym, sympod; vp, ventral process. [A, B, after
Lagardère, 1983; C, after Murano, 1988; D, Q, after G. O. Sars, 1879; E-H, after G. O. Sars, 1877;
J, after Tattersall & Tattersall, 1951; K, after Băcescu, 1968b; L, after Wittmann, 2009; M, after G.
O. Sars, 1885a; N, after Wittmann, 1986a; O, after Wittmann & Ariani, 2012a; P, after G. O. Sars,
1893; R, S, after Wittmann, 2008; T, after Lagardère & Nouvel, 1980b; U, after Hanamura & Kase,
2003.] [A, D, J-N setae omitted; A-Q, T, U, modified.]
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Fig. 54.22. Uropods, telson, and associated structures in the Lophogastrida families Lophogastridae
(A, B), Eucopiidae (C), and Gnathophausiidae (D, E); in the Stygiomysida families Stygiomysidae
(F) and Lepidomysidae (G, H); and in the Mysida families Petalophthalmidae (J) and Mysidae
(K-O); dorsal view unless stated otherwise. A, Lophogaster typicus M. Sars, 1857; B, Ceratolepis
hamata G. O. Sars, 1883; C, Eucopia australis Dana, 1852; D, Gnathophausia ingens (Dohrn,
1870); E, Gnathophausia ingens, epimeron from the sixth pleonite, ventral; F, appendages of the
pleomeres 5 and 6 in Stygiomysis holthuisi (Gordon, 1958), ventral; G, Spelaeomysis cardisomae Bowman, 1973, uropods, ventral; H, Spelaeomysis bottazzii Caroli, 1924; J, Petalophthalmus
armiger Willemoës-Suhm, 1875; K, Rhopalophthalmus longicauda O. S. Tattersall, 1957; L, Siriella
gracilis Dana, 1852; M, Mysidetes intermedia O. S. Tattersall, 1955; N, Mysidopsis robustispina
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remaining subfamilies of the Mysidae (fig. 54.22M, N). Its margins may be entirely lined
by setae, may be smooth, or (in part) armed with spines or spine-like setae. The endopod
has a well-developed transverse suture only in the Rhopalophthalminae; this suture is at
about one quarter endopod length from the tip. This subfamily is exceptional in having
both rami of the uropods subdivided (fig. 54.22K). In Mysidae, the apical portions of the
endopod are mostly narrower than those of the exopod (fig. 54.22K, L). The basal portions
of the endopod are swollen to accommodate the usually large, globular statocyst (fig.
54.22K-O; see below, ‘Sensory organs’).
INTERNAL MORPHOLOGY
The main internal organs of the Mysida are located in the cephalothorax as shown in
fig. 54.23 for females (A) and males (B).
Musculature
Wollner (1924) described the complex musculature responsible for the movements of
antennae, eyestalks, and mouthparts. The body musculature is also quite complex and
composed of a system of metamerically arranged muscles: dorsal, latero-dorsal, ventral,
and superficial-ventral muscles, plus basal extensors and flexors of the appendages. Detailed descriptions are given by Daniel (1928, 1933) for the lophogastrids Gnathophausia
zoea and Lophogaster typicus, and for the mysid Praunus flexuosus. His meticulous figures
are reproduced and discussed in the review by Mauchline (1980) (see also Manton, 1928a;
Needham, 1937; Mayrat, 1955, 1956b). The musculature inserts partly on a non-chitinous
internal skeleton including an endosternite, tendons, and columns (Debaisieux, 1954).
According to Nath (1974), the cavernicolous Stygiomysida Spelaeomysis longipes shows
a simplified musculature probably due to reduced swimming activity and the resulting
atrophy of muscles otherwise used by epigean species for swimming.
Nervous system
Neural chain. – The gross morphology of the nervous system (fig. 54.24) of the
Mysida and Lophogastrida was described so far by only few authors (G. O. Sars,
1867, 1885a; Illig, 1912). Our knowledge is still rudimentary compared with that about
the Decapoda (Harzsch et al., 2012). The cerebral ganglia or brain are differentiated
into protocerebrum, deutocerebrum, and tritocerebrum, with a post-oesophageal
Brattegard, 1969, ventral; O, Diamysis bahirensis (G. O. Sars, 1877), terminal portion of sixth
pleonite, lateral. Abbreviations: an, anus; ils, inner lobe from sympod of uropods; sc, scutellum
paracaudale; sl5, sternal lamellae from pleonite 5; stc, statocyst; stl, statolith; tl, telson. [A-E, J, L,
after G. O. Sars, 1885a; F, after Gordon, 1960; G, after Bowman, 1973; H, after Ariani, 1981c; K,
after O. S. Tattersall, 1957; M, after O. S. Tattersall, 1955; N, after Brattegard, 1973; O, original,
adult female from the El Bahira lagoon at the Mediterranean coast of Tunisia.] [A, D, J, M, N setae
(partly) omitted; F-N, modified.]
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Fig. 54.23. Localization of the main internal organs in Mysida, schematic. A, female Mysis relicta
Lovén, 1862, sagittal view; B, transverse section through thorax of male Praunus flexuosus (O. F.
Müller, 1776). Abbreviations: aa, abdominal aorta; c, carapace; ha, heart; he, hepatopancreas; in,
intestine; ms, muscles; nt, nerve tract; od, oviduct; ot, ovarian tubes; sto, stomach; tst, testicles; sv,
seminal vesicle. [After Nouvel et al., 1999, based on G. O. Sars, 1867 (A) and Labat, 1961 (B).]
commissure, and are located above and in front of the mouth. The paired optical,
antennular, and antennal nerves depart from the anterior portion of the cephalic mass; this
mass is connected by the peri-oesophageal connectives with the ventral ganglion chain.
Within this chain the paired ganglia are tightly interconnected medially. These connectives
are generally distinct. A primitive situation is found in the mysid Birsteiniamysis inermis
(fig. 54.24C): the ganglion masses related to the mouthparts are well separated with short
connectives; their chain is continued by eight ganglion masses related to the thoracopods,
plus six masses for the pleon. These elements are generally more condensed in the other
species that have been studied. In the mysid Mysis relicta (fig. 54.24B), the eleven postcerebral masses of the cephalothorax are reduced to ten by fusion of the two anterior ones.
These ten masses are still discernible within the long band of ganglia. In the lophogastrid
Eucopia (fig. 54.24A), the first pair of thoracic ganglia is more or less integrated into
the single extended ganglion mass innervating the mouthparts; moreover, the ganglia of
the eighth pair are smaller and more tightly interconnected, thus resembling the ganglion
masses of the pleon. This resemblance is underlined by the visual aspect of the neural
chain, which shows a distinct change between thoracomeres 7 and 8: short distances
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Fig. 54.24. The nervous system in Lophogastrida (A) and Mysida (B-D). A-C, neural chain in
Eucopia sculpticauda Faxon, 1893 (A), Mysis relicta Lovén, 1862 (B), and Birsteiniamysis inermis
(Willemoës-Suhm, 1874) (C), symbols indicate targets innervated by respective ganglia; D, neuropils
and neurosecretory centres in eyestalk of Siriella armata (H. Milne Edwards, 1837), strongly
schematic dorsoventral section, the graphic symbols indicate different types of neurosecretory
cells. Abbreviations: a2, antennal nerve; bs, blood sinus; la, lamina; lob, lobula; med, medulla;
miX, medulla interna and externa X-organ; mt, medulla terminalis; mtX, medulla terminalis Xorgan; oB, organ of Bellonci; p1-p6, ganglia innervating pleomeres 1-6; sg, sinus gland; t1-t8,
ganglia innervating thoracomeres 1-8. [A, C, modified after G. O. Sars, 1885a, originally named
Gnathophausia longispina (A) or Boreomysis scyphops (C), respectively; B, after G. O. Sars, 1867;
D, after Cuzin-Roudy & Saleuddin, 1985, with permission by “© Canadian Science Publishing or
its licensors”, Ottawa.]
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between the pairs of ganglia and a distinct space between left and right neural chains in
front of this limit, but longer distances between consecutive ganglia and medially tightly
adjoining neural chains behind. Such differences between thorax and pleon are generally
found in Lophogastrida. This explains the error by G. O. Sars (1885a: pl. X fig. 12), who
mistook the ganglia of the ultimate thoracomere as pertaining to the first pleomere. An
additional error by G. O. Sars (1885a: pl. VIII fig. 19) regards the nervous system of
Gnathophausia, where one among the eight thoracic ganglia is missing and the first one is
figured as pertaining to the mouthparts despite being actually well separated. Exactly this
error justifies reproducing the anterior part of his drawing, although it must be attributed
to a different genus, namely Eucopia, with which it shows an astonishing coincidence
(fig. 54.24A). In both genera, the ultimate ganglion mass of the pleon is more strongly
developed compared with the preceding one, probably as a consequence of the fusion of
the sixth and seventh pleomeres.
Brain and associated organs. – The histology of the brain, the ganglia in the eyestalks,
and associated sense organs and endocrine glands were studied by Hanström (1947,
1948), Mayrat (1956a), Hogstad (1969), Elofsson & Dahl (1970), Strausfeld & Nässel
(1981), Cuzin-Roudy & Saleuddin (1985), and Elofsson & Hagberg (1986). Only a short
summary is given here beyond the gross structures of the neural chain mentioned above:
The pons protocerebralis with the central body (corpus centrale) of the protocerebrum are both homogeneous in Lophogastrida, but divided into glomeruli in Mysida.
The glomerular paracentral lobe is broadly connected with the central body and shows
strong commissures. A median frontal organ is known only from the lophogastrid Eucopia (Hanström, 1947). It is inside the frontal plate and may attain a considerable size;
each of several cell pairs forms an acidophilic plaquette. No naupliar eye is present in
Lophogastrida, Stygiomysida, or Mysida. In the deutocerebrum, the layer of ganglion
cells contains a group of cells related to the olfactory lobes, more strongly developed in
Lophogastrida than in Mysida. The antennular fibres end in the glomeruli of the olfactory
and the parolfactory lobes; a large unpaired glomerulus appears to be a peculiarity of the
Lophogastrida and to have no equivalent in other crustaceans.
Optic ganglia. – The optic ganglia are located in the eyestalks in all taxa (fig. 54.24D).
They include three columnar optic neuropils and the medulla terminalis as prolongations
of the protocerebrum. As in insects, the three neuropils are currently termed — in inwarddirected series — lamina, medulla, and lobula (Strausfeld & Nässel, 1981; Harzsch
et al., 2012), whereas previously in a more crustacean-focused approach as lamina
ganglionaris, medulla externa, and medulla interna (Elofsson & Dahl, 1970; CuzinRoudy & Saleuddin, 1985; Nouvel et al., 1999). The sinus gland is a discoid thickening of
the medulla terminalis at the level of a large blood sinus in the lophogastrids Eucopia and
Gnathophausia and in the mysids Boreomysis and Mysis. In these genera it is separated
from the neuropil by a layer of cellular bodies, but not so in the mysid genus Praunus. The
sinus gland of the mysid Siriella armata extends externo-ventrally over medulla terminalis
and lobula (fig. 54.24D; Cuzin-Roudy & Saleuddin, 1985). Like most malacostracans,
the lophogastrids and mysids also have two chiasmata in the eyestalk, the distal one
between lamina and medulla, the proximal one between medulla and lobula. The proximal
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chiasma may be indistinct in reduced eyes due to the tendency of the proximal neuropils
to withdraw into the brain (Elofsson & Dahl, 1970).
Using immunohistochemical methods, Benzid et al. (2006) found different signals of
the neurotransmitter serotonin in the lamina after a dark to light illumination change
versus a light to dark change in the diurnally migrating mysid Hemimysis speluncola.
No such difference was recorded in the non-migrating Leptomysis lingvura. The authors
concluded that the lamina can function as a photoreception signal integrator during
phases of illumination change.
Organ of Bellonci. – This organ, also termed ‘sensory papilla X-organ’ (SPXorgan), is found in most crustaceans (Hallberg & Chaigneau, 2004). In Lophogastrida
and Mysida, it is located directly under the dorsal cuticle near the base of the eyestalk
(figs. 54.24D, 54.25E) or, if present, near the base of eyestalk papillae (Hanström, 1947;
Mayrat, 1956a; Dahl & von Mecklenburg, 1969; Hogstad, 1969; Kauri & Dahl, 1975;
Cuzin-Roudy & Saleuddin, 1985). Dahl & von Mecklenburg (1969) described the organ
of Bellonci as a group of cells and a vesicle surrounded by a connective tissue sheath
near the base of the eyestalk papilla in Boreomysis arctica and assumed neurosecretory
and neurohaemal functions. Re-examination by Kauri & Dahl (1975) revealed sensory
neurons with ramifying cilia branches protruding into the cavity, thus pointing rather to a
sensory function. The organ is distally connected with a nerve coming from the eyestalk
papilla, and proximally with a nerve entering the medulla terminalis. In most species
of the family Mysidae, the eyestalk papillae show a great morphological diversity up to
reduction or complete absence (fig. 54.25). For example in Siriella armata, the organ
of Bellonci represents a single cavity near the base of the eyestalk (fig. 54.24D; CuzinRoudy & Saleuddin, 1985). This cavity is lined by sensory cells that, with their axonlike elongations, extend to the medulla terminalis. The cavity is probably analogous to
the structure Stammer (1936) interpreted as a rudiment of lenses in the cavernicolous,
anophthalmic mysid Troglomysis vjetrenicensis. A chemosensory or else a photosensitive
function of the organ of Bellonci is assumed for most crustaceans (Hallberg & Chaigneau,
2004), but its precise functions still remain unknown for Lophogastrida and Mysida.
Despite its homonymous designation as ‘X-organ’ by many authors, the organ of Bellonci
is not identical with the neurosecretory organs of the eyestalk, termed “ME-MI X-organ”
and “MT X-organ” by Cuzin-Roudy & Saleuddin (1985) (fig. 54.24D; see also below,
‘Endocrine organs’).
Sensory organs
E YES AND VISION
Gross morphology of the eyes (fig. 54.25). – The compound eyes are each borne by
a cylindrical or almost conical, more or less elongate mobile eyestalk. The cornea is
generally globular, hemispheric, occasionally reniform. Birsteiniamysis inermis has quite
particular eyes: cup-shaped, with about 3000 ommatidia (Elofsson & Hallberg, 1977,
as Boreomysis scyphops). In several bathypelagic Mysidae, e.g., in Euchaetomera and
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Caesaromysis, and in epipelagic Carnegieomysis, the cornea is divided into a frontal and
a lateral cornea, more or less separated, sometimes widely separate (fig. 54.25G); it is
in part formed by two types of visual elements with probably different visual function.
The latero-posterior ommatidia are much larger than the frontal ones in the subdivided
cornea of Paraleptomysis (fig. 54.25H). Although pertaining to different subfamilies,
Leptomysinae and Mysinae, respectively, the genera Dioptromysis and Kainommatomysis
have in common a very large, specialized latero-posterior lens (fig. 54.25F), separated from
the frontal cornea. According to Nilsson & Modlin (1994), in Dioptromysis paucispinosa
this lens consists of a large facet over an equally enlarged crystalline cone, projecting an
image onto a specialized retina with 120 densely packed, extremely narrow rhabdomes
(eye structure by Land, 2004, reproduced in fig. 6.22 of the present series). The centre
of this zone performs six times better than the normal eye and covers a visual field of
15-20° with large binocular overlap, in good analogy with a pair of binoculars. With
appropriate eyestalk movements the acute zone can to a limited extent face forwards
and upwards, according to the interpretation by Nilsson & Modlin (1994) in favourable
direction for spotting prey. For this species, however, and also for its Red Sea counterpart
Kainommatomysis schieckei, there is no published evidence for a predatory mode of life.
A few specimens of the latter species were studied by one of us (KJW) in the Gulf of
Sinai and the Gulf of Aqaba. Besides eye morphology, they shared with the Caribbean
Dioptromysis paucispinosa an epibenthic lifestyle during daytime and stomachs that
contained diatoms and remains of other microalgae, but no animal remains. Thus, the
eco-physiological context of the binocular-like eye modifications remains obscure.
Structure of the cornea. – As in the Euphausiacea, the compound eyes of Mysida are
of the refracting superposition type (Strausfeld & Nässel, 1981; Nilsson & Modlin,
1994; Land, 2004). The cornea is formed by juxtaposed ommatidia showing (Parker,
1891; Chun, 1896; Mayrat, 1956a; Elofsson & Hallberg, 1977; Hallberg, 1977) similar
numbers of cells as in decapods. Each ommatidium contains a vaulted lens, representing
a transparent part of the cuticle secreted by two corneagenous cells. Above there is a
crystalline cone with its large basis turned to the cornea, comprising two compound
halves. Among the four crystalline cells only two secrete each a half cone into their
cytoplasm. A short axial crystalline tract, formed by four crystalline cells, penetrates a
short distance. The retinula contains eight (Mysidopsis, Praunus, Siriella) or only seven
(Erythrops, Neomysis) photoreceptor cells (Hallberg, 1977; Strausfeld & Nässel, 1981),
one of which is the most voluminous, while another, the accessory cell, penetrates into the
axis. All except the latter are prolonged by a nerve fibre. The relatively short rhabdome is
connected with the crystalline tract by a crystalline formation, the epirhabdome (absent
in Erythrops); the latter consists of four branches which surround the accessory retinula
cell and reunite on the top of the rhabdome (Hallberg, 1977). The rhabdome appears to
be formed by eight chitinous, serrate, intricate rhabdomeres, secreted by the retinula
cells. It is fused and banded as in decapods and euphausiaceans (Strausfeld & Nässel,
1981). Screening pigment cells surround the crystalline part and the proximal portions of
the retinula cells, and contain a melanin pigment that becomes particularly dense around
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the rhabdome. The granules of the distal and proximal reflecting pigment cells probably
contain pteridine. There is a wide clear zone between the cones and the rhabdomes. Rays
entering from many facets can be brought into focus in this zone. Pigment migration for
dark and light adaptation in the compound eye is similar to that described for decapods
(Hallberg et al., 1980). The migration ranges of the screening pigments are relatively small,
always leaving a clear zone between distal and proximal pigment cells. The proximal part
of the crystalline cones is more pointed in the light- versus the dark-adapted eye.
The numbers of ommatidia vary considerably between the various species of Mysida
and Lophogastrida, according to Mauchline (1980) without recognizable, consistent
reasons. By contrast, differences between populations of the same species may be
explained by the different light intensities they experience in nature. According to J.-P.
Casanova (1977), the lophogastrid Eucopia unguiculata shows degenerate eyes, but the
Atlantic specimens have larger eyes with more ommatidia compared to Mediterranean
specimens sampled by him in the same depth but at lower light intensity.
Vision. – According to Beeton (1959), the mysid Mysis diluviana is sensitive to
wave lengths of 515 and 395 nm, probably in correspondence with two different visual
pigments. Lindström & Nilsson (1988) argued that geographically isolated populations of
“Mysis relicta” may show different spectral sensitivity and tolerance to light intensity,
but actually this may reflect differences between separate species described much later
by Audzijonyte & Väinölä (2005, 2006): Mysis salemaai from brackish waters of the
Baltic versus Mysis relicta from freshwater lakes in Scandinavia. Laboratory experiments
on seven Baltic species of mysids by Lindström (2000) showed that the eye spectral
sensitivity differs in accordance with wavelength-shifts in light transmittance of the water
bodies from which the respective test specimens were taken. The eyes of Mysis relicta
from Lake Pääjärvi (Finland) responded to near-infrared light, their spectral sensitivity
being among the most red-shifted known (Lindström & Meyer-Rochow, 1987; Lindström,
2000). The experiments of Moeller & Case (1995) on the lophogastrid Gnathophausia
ingens indicated differences in visual function, particularly regarding circadian rhythms
of visual sensibility, between juveniles and adults. This is related to the shallower habitat
of the juveniles.
According to Hallberg et al. (1980), the screening pigments of Neomysis integer
need about 20 minutes to migrate upon light-adaptation, but more than one hour upon
dark-adaptation. The position of the pigment in light-adapted eyes varies with light
intensity. Those authors observed no cyclic diurnal pigment migrations in animals kept
either permanently in total darkness or under continuous illumination. Lindström (1992,
2000) found that the eyes of Mysis relicta are easily damaged by strong light intensity;
particularly if the specimens were forced from the dark deep waters of freshwater lakes
to the bright daytime light at the surface upon sampling. Feldman et al. (2010) reported
higher concentrations of retinol and other retinoids in a Mysis relicta population from
the same (above quoted) dark, deep, freshwater Lake Pääjärvi, compared to animals from
more shallow waters in the Baltic Sea. This points to a larger storage of chromophores or
precursors for dark regeneration of visual pigment. Suddenly exposing the lake animals
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Fig. 54.25. The diversity of eye modifications in Lophogastrida (A, B), Stygiomysida (C, D),
and Mysida (E-P). A, Paralophogaster foresti Băcescu, 1981; B, Eucopia major Hansen, 1910;
C, Spelaeomysis cochinensis Panampunnayil & Viswakumar, 1991; D, Spelaeomysis olivae
Bowman, 1973; E, Diamysis lagunaris Ariani & Wittmann, 2000; F, Dioptromysis perspicillata
Zimmer, 1915; G, Euchaetomera zurstrasseni (Illig, 1906); H, Paraleptomysis dimorpha Wittmann,
1986, female; J, Heteromysoides cotti (Calman, 1932); K, Antromysis cubanica Băcescu &
Orghidan, 1971; L, Birsteiniamysis inermis (Willemoës-Suhm, 1874); M, Ceratomysis spinosa
Faxon, 1893; N, Petalophthalmus armiger Willemoës-Suhm, 1875; O, Dactylerythrops dactylops
Holt & Tattersall, 1905; P, Pseudomma affine G. O. Sars, 1870. Abbreviations: eyp, eyestalk
papilla; fp, fenestra paracornealis; oB, organ of Bellonci. [A, after Băcescu, 1981; B, after
Nouvel, 1943; C, after Panampunnayil & Viswakumar, 1991, permission granted by Springer
Verlag, Vienna; D, after Bowman, 1973; E, after Wittmann & Ariani, 2012a; F, after Zimmer,
245
to stronger light could induce massive pigment activation and resulting photoreceptor
damage. Similar laboratory results were obtained by Attramadal et al. (1985): the marine
deep-water (mesopelagic) mysid Boreomysis megalops showed pathological changes in
eye morphology as well as abnormal vertical zonation behaviour after exposure to surface
daylight. These findings on Mysis and Boreomysis raise strong questions about earlier
works on vision and behaviour of deep-water species if the experimental specimens were
exposed to bright light upon sampling and/or experimentation.
Eye reduction (fig. 54.25C, D, J-P). – The cornea is often reduced to a small number
of ommatidia with often rudimentary structure, and the pigment may have disappeared
completely in deep-water and cavernicolous species, clearly in relation to the poor light
conditions of their habitat. The cavernicolous mysid Heteromysoides cotti (fig. 54.25J)
from marine lavatunnels at Lanzarote (Canary Islands) has small eyes with at most 30
ommatidia. According to an electron microscopic study by Meyer-Rochow & JuberthieJupeau (1987), these ommatidia show signs of degeneration; the eyes are probably not
equipped with any polarization sensitivity and incapable of form vision, but may be able
to distinguish different light intensities and possibly also the direction of light. The loss of
visual abilities appears to be counterbalanced by more effective tactile and chemosensory
abilities in subterranean mysids (cf. Crouau, 1981).
The various species are not affected in the same way by the light conditions of their
environment, and factors associated with phyletic lineages probably play some role. Thus,
in the lophogastrid genus Eucopia, most species show a rather small cornea (fig. 54.25B).
This is less evident in Eucopia sculpticauda, despite its preference for deep waters. This
species is considered to be the most primitive in its genus as indicated by morphological,
anatomical, and molecular characters (J.-P. Casanova et al., 1998); it is positioned near
species of Gnathophausiidae, which all have normally developed eyes. More or less
pronounced eye reductions have been observed in about one tenth of the known species.
This is typically correlated with eyestalk modifications (Stammer, 1936; Zharkova, 1970;
Nath et al., 1972a).
The generally subterranean stygiomysid genus Spelaeomysis shows various degrees of
eye reduction, both between adults of different species and during the course of marsupial
development. In adults of most species the eyes are reduced to tile-like plates (fused to
a single median eye plate in Spelaeomysis longipes) without any trace of pigment, but
Spelaeomysis cardisomae has distally widened, latero-distally well-pigmented (fig. 54.3B)
eyestalks with only a few ommatidia (Bowman, 1973). In Spelaeomysis nuniezi only the
postnauplioid larvae show almost normal eyes (Ortiz et al., 2005), but the adults have the
eyes reduced to sub-quadrangular plates completely lacking cornea and pigment (Băcescu
& Orghidan, 1971). Also in Spelaeomysis bottazzii, both adults and juveniles (fig. 54.38K)
1915; G, after Illig, 1930; H, after Wittmann, 1986c; J, after Calman, 1932; K, after Băcescu &
Orghidan, 1971; L, after Hansen, 1908; M, after Faxon, 1895; N, after W. M. Tattersall, 1925 (scale
derived from Tattersall & Tattersall, 1951); O, after Holt & Tattersall, 1905; P, after G. O. Sars, 1870;
A, D-O, modified.]
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Fig. 54.26. Statocyst allocation and structure in Mysidae (Mysida). A, allocation of the statocyst
in uropodal endopods of female Siriella gracilipes H. Nouvel, 1942, lateral view (setae partly
omitted), right statolith indicated as black ellipsoid; B, schema of statocyst in Neomysis integer
(Leach, 1814); C, schematic cross section through tail fan of Siriella clausii G. O. Sars, 1877, at
height of statolith; D, groups (a-e) of non-sensory apical portions of sensory setae entering left
statolith of Siriella clausii, ventral view; E, semi-schematic longitudinal section through uropod of
247
have the eyes reduced to unpigmented plates, but the postnauplioids are still showing
almost cylindrical stalks with pale cornea (fig. 54.38J; Ariani & Wittman, 2010).
Eyestalks nearly or completely fused to a single median eye plate are also found
in certain Mysida, such as the Mysidae Pseudomma (fig. 54.25P), Parapseudomma,
Calyptomma, and Michthyops. Occasionally the eye plate may be hidden by the frontal
plate as in the Petalophthalmidae Hansenomysis and Bacescomysis.
Additional eye-related structures. – The eyestalks are often furnished with a fingerlike, mostly lateral sensory papilla of variable size (fig. 54.25A, B, G, O). In the
lophogastrid Paralophogaster foresti, this papilla is remarkably large, often exceeding the
diameter of the cornea (fig. 54.25A; Băcescu, 1981). A small basal ganglion, connected
with the optic centres, sends its prolongations to this organ, which in certain taxa may
be reduced from a papilla to a sensory pore. In the mysid Boreomysis a nerve from the
papilla innervates the organ of Bellonci (see above). The detailed function of the eyestalk
papillae is still unknown. A fenestra paracornealis, i.e., a pale, pigment-free, rounded
and slightly elevated spot on the eyestalks near the cornea, has been described in certain
species of the mysid genus Diamysis (figs. 54.12D, 54.25E; Ariani & Wittmann, 2000). An
additional one is associated with the organ of Bellonci, located dorsally near the inner basal
corner of the eyestalks. The visibility of these features depends on the state of preservation
(may be invisible in old museum specimens), as well as on the pigment richness of the
eyestalk surface. Branches of eyestalk chromatophores may surround but do not extend
over these fenestrae, often resulting in a striking colour contrast to the surrounding parts
of the eyestalk. A series of a few separate ommatidia may be present along the distal
margin of the fenestra (fig. 54.25E). After bleaching in Swan-medium, a ganglion mass
becomes visible below the fenestra paracornealis; this mass is similar in size and structure
to that of the organ of Bellonci. Both fenestrae clearly favour light penetration to sensory
organs. Prolonged bleaching revealed that the ganglion mass associated with the fenestra
paracornealis is present in many (possibly all) Diamysis species, but that parts of it are
often located below the cornea.
S TATIC ORGANS
Statocyst structure (fig. 54.26). – Statocysts are present only in the family Mysidae
(G. O. Sars, 1867; Bethe, 1895; Debaisieux, 1947, 1949a; Espeel, 1985; Schlacher et al.,
1992; Ariani et al., 1993), where they are located at the base of the endopods of the
uropods. They consist of a large vesicle formed as an invagination of the integument.
Praunus flexuosus (O. F. Müller, 1776); F, basis of right uropodal endopod in Diamysis mesohalobia
Ariani & Wittmann, 2000, fresh preparation in ambient water 55 min after moult, core (co) showing
incipient mineralization, (a-e) groups of sensory setae, dorsal dark-field aspect. Abbreviations: am,
ambitus; co, core; end, endopod of uropod; ex, exopod of uropod; fu, fundus; ma, mantle; ms,
muscle; ne, nerv; sca, statocyst cavity; scl, statocyst slit; sec, sensory cushion; ses, sensory setae; stl,
statolith; sym, sympod of uropods; tg, tegmen; tl, telson. [A, after Wittmann et al., 1993, permission
granted by John Wiley & Sons, Ltd., Hoboken; B, after Espeel, 1985; C, D, after Schlacher et al.,
1992; E, after Debaisieux, 1949a; F, after Ariani et al., 1982; B, C, modified; D, permission granted
by Springer Verlag, Vienna.]
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The cavity is entirely lined by cuticle and contains ambient water. It is connected with
the outside milieu through the statocyst slit. Its cuticle is entirely shed upon each moult.
A small muscular bundle, extending from the external wall of the uropod to the statocyst,
apparently adjusts the tension in the latter. The ventral wall of the cavity bears a sensory
cushion: an arch of sensory setae penetrating with their non-sensory distal portions from
below into a usually large, complex statolith. A few comparatively large setae emerge from
the posterior part of this arch, and more, mostly smaller ones, from the outer anterior part.
The setae are organized in serial groups along this arch, indicated by (a-e) in fig. 54.26D,
F. The setae are shed at moulting together with the cuticle. According to Espeel (1986), the
sensitivity of the sensory cells of the old setae is maintained until the moment of ecdysis.
Statolith composition and structure (fig. 54.27A-G). – In most Mysidae, each statolith
consists (Wittmann et al., 1993) of two distinct parts. The first is the core (nucleus).
Usually it contains both organic and mineral materials. It is rarely exclusively organic
as erroneously believed in early works on species with fluorite statoliths. The second is the
mantle, almost entirely mineralized with fluorite (CaF2 ; fig. 54.27D, E). In a relatively
small number of species, the mantle is mineralized with calcium carbonate (CaCO3 ) in the
metastable crystal phase of vaterite (fig. 54.27B, F; Ariani et al., 1993). Vaterite statoliths
have so far been found in only seven genera of the subfamily Mysinae. Carbonate mysid
statoliths in the stable crystal phase of calcite (fig. 54.27C, G), however, are known from
Miocene deposits of eastern Europe, which was covered at that time by the extensive
brackish basin of the Paratethys (Voicu, 1974, 1981). The finding of calcite in all examined
Paratethyan fossils and in a few aged museum specimens of (otherwise vaterite-bearing)
extant species, suggests that the calcite content is normally produced post mortem by
spontaneous phase transformation of the originally present metastable vaterite to the stable
calcite during fossilization and/or long-term storage (Wittmann et al., 1993).
Unlike in extant fluorite statoliths (fig. 54.27D), the core is mostly not covered ventrally
by the mantle in both Recent and fossil carbonate statoliths (fig. 54.27B, C). Note also the
strong similarity between the statoliths of the extant Paramysis lacustris (fig. 54.27B) and
those obtained from Miocene Paratethys sediments (fig. 54.27C). Any type of carbonate
statoliths may show a central, non-mineralized cavity within the core. The relative size
of the central cavity tends to increase with individual size of the statolith and may open
ventrally to the exterior as a hole in about central position. This hole, named hilum (hi),
is still rather small in fig. 54.27B, but figures of much more prominent hila are available
in Wittmann et al. (1993). The entry points of the apical parts of the sensory setae into
the statoliths mark a semi-circular series of pores with diameters decreasing (in ventral
view) in clockwise or anticlockwise order, according to left (fig. 54.27A, D) or right
(fig. 54.27B, C) statoliths, respectively. These pores appear to be arranged in distinct
groups, thus allowing to derive a characteristic statolith formula (Voicu, 1974), such as
2 + 3 + 1 + d + e = n, where d and e indicate groups with variable numbers of pores, and n
the total number of pores (Wittmann, 1992a). Extensive investigations by Schlacher et al.
(1992), however, showed that only the first 2-3 groups of pores may have some taxonomic
value, although even the configuration of these groups is rarely exclusive for a single genus.
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Fig. 54.27. Structure (A-D), mineral composition (E-G), and formation (H-K) of statoliths in recent
(A, B, D-F, H-K) and fossil (C, G) Mysidae (Mysida). A-D, ventral aspects of statoliths in toto, SEMimages; A, non-mineral (organic) left statolith of Rhopalophthalmus terranatalis O. S. Tattersall,
1957; B, right vaterite statolith in Paramysis lacustris (Czerniavsky, 1882); C, right fossil calcite
statolith from Upper Miocene deposits of the brackish Paratethys, short arrows point to selected
pores along pore arch of lith; D, left fluorite statolith of Haplostylus magnilobatus (Băcescu &
Schiecke, 1974); E-G, SEM-images of mineral structures from outer surface (E, F) and/or artificial
fracture surfaces (E, G), respectively; E, cubic crystal habits of fluorite in Mysidium integrum W. M.
Tattersall, 1951; F, needle-like vaterite aggregates in Schistomysis assimilis (G. O. Sars, 1877);
G, rhombohedral crystal habits of calcite in fossil statolith as in (C); H-K, vaterite mineralization
of organic matrix in time series of 12, 48, and 180 min, respectively, after moult in Diamysis
mesohalobia Ariani & Wittmann, 2000, diascopic dark-field aspects of fresh preparations in ambient
water. Abbreviations: hi, hilum; om, organic matrix; ses, sensory setae. [A, after Schlacher et al.,
1992, permission granted by Springer Verlag, Vienna; B, D, photo Thomas Schlacher & Karl J.
Wittmann; C, E-G, after Wittmann et al., 1993, permission granted by John Wiley & Sons, Ltd.,
Hoboken; H-K, after Ariani et al., 1982.]
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A further type of static bodies is non-crystalline, organic statoliths (fig. 54.27A), peculiar
to the primitive subfamilies Boreomysinae and Rhopalophthalminae (Ariani et al., 1993).
A study at worldwide scale (Ariani et al., 1993) revealed correlations between crystallographic characteristics of statoliths, and the ecology and biogeography of mysids: fluorite precipitation apparently prevails in the sea. Vaterite was mainly found in fresh and
brackish waters, non-crystalline statoliths predominantly in the deep sea (except for the
coastal Rhopalophthalminae). The vaterite precipitation in most species of Diamysis and
Paramysis, which today inhabit the Mediterranean and Black Sea basins, was considered
indicative of a Paratethyan origin: the ancestors of these taxa are thought (Ariani, 1981a;
Wittmann & Ariani, 2011) to have been drained into the Mediterranean as a consequence
of the Mediterranean salinity crisis (Hsü et al., 1977).
Statolith formation (fig. 54.27H-K). – Unlike the statoliths of Decapoda, the static
bodies of the Mysidae (Mysida) are endogenous and renewed upon each moult. As a
phylogenetic-ontogenetic parallel, an organic matrix is formed before the start of the
mineralization process, as shown by the laboratory study of Ariani et al. (1982) on
the formation of vaterite statoliths in Diamysis. In these experiments, the statoliths were
formed within only a few hours after moulting (fig. 54.27H-K). The organic matrix consists
of acid mucopolysaccharides and glycoproteins (Ariani et al., 1982) in the vaterite
statoliths of Diamysis, but mainly of sulphated mucopolysaccharides (Espeel, 1987) in the
fluorite statoliths of Neomysis. Wittmann & Ariani (1996) determined the concentration
factors of ions, particularly fluoride (F− ), invested into the renewal of the statolith.
A typical fluorite statolith contains about 180 000 times the amount of fluorine present
in the seawater contained in the statocyst. So far, detailed sources and uptake of ions for
statolith formation remain obscure. Ariani et al. (1999) experimentally investigated the
role of the organic matrix for the renewal of vaterite statoliths at moulting in a species
of Diamysis. This involved using an inhibitor (acetazolamide) of carbonic anhydrase or
a generically toxic substance (ethanol) for comparison. Under both these conditions the
mineral precipitation was not stopped, but in a few cases there was in vivo precipitation of
calcite instead of vaterite, possibly correlated to failure of, or damage to, the organic frame
that mediates the mineralization process.
Statocyst function. – Early authors attributed auditory functions to the statocyst,
consequently erroneously describing it as “otocyst”. They were not completely wrong,
as sensitivity to vibrations is not excluded (Cohen, 1955). Delage (1887) was the first to
suggest that the statocyst is sensitive to the action exerted by the weight (actually also the
inertia) of the statolith and that the perceptions by the sensory setae are determinants of
locomotor reflexes for orientation. Today, the statocyst is generally seen as an equilibrium
organ for stabilization of body position and for directional swimming. Laboratory studies
by Schöne (1954) for decapods and by Neil (1975a, b) for the mysid Praunus flexuosus
demonstrated that the right and left statocysts co-operate in controlling the eyestalk
movements. This shows that a major function of mysid statocysts is stabilization of the
visual field, as is generally known for static organs in visually oriented animals, also
in humans. In line with this, Mysinae with well-developed eyes generally have large
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statoliths, whereas species with reduced eyes have on the average smaller ones, and those
without any visual elements again smaller ones (Wittmann et al., 1990). Correspondingly,
the diameter of fluorite statoliths is generally larger in species of Mysinae from lightexposed, epipelagic and coastal habitats as compared to darker, deep-water habitats; the
epipelagic species of Siriellinae have mostly larger statoliths compared to the neritic
species. Together with landmarks perceived by the visual system, the statocysts are also
involved in the perception of water currents, helping to guide the horizontal migration
of Hemimysis speluncola back into dark submarine caves at daybreak (Passelaigue &
Bourdillon, 1986; Passelaigue, 1989).
S ENSORY SETAE
Diversity of sensory setae. – Many types of sensory setae (fig. 54.28) in Mysida
and Lophogastrida are located on various parts of the integument (Debaisieux, 1947,
1949a, b; Crouau, 1978a, 1981, 1989; Johansson & Hallberg, 1992; Johansson et al.,
1996). They are particularly abundant on the antennulae, antennae, and mouthparts,
as well as on the locomotory appendages. Some are plumose and may be important
for hovering, others are smooth or barbed and may have diverse, in some cases still
hypothetical, functions, particularly as aesthetascs (olfactory hairs) or as tactile organs
(mechanoreceptors). Crouau (1981) found 18 different types of setae on the antennulae
and antennae in laboratory specimens of the tropical, subterranean, anophthalmic mysid
Antromysis juberthiei. In 1987, the same author reported only 12 different types on the
mouthparts and thoracic endopods of the same species, yet with greater morphological
differences between these types (fig. 54.28). In 1989, he grouped these 12 types in the
categories of plumose (fig. 54.28F-H), serrulate (M-R), pappose (J), small (K), and pushing
(L) setae.
Mechanoreceptors. – According to Crouau (1978b, 1979), the mechanoreceptors
on the antennula of Antromysis juberthiei respond to tactile and hydrodynamic stimuli,
including waterborne vibrations and turbulences. Hallberg & Chaigneau (2004) interpreted
the perception of vibrations as a kind of hearing, thus as a useful adaptation for
localization of prey by these subterranean, anophthalmic mysids. Crouau (1982) presented
a detailed hypothesis on how the initially mechanical signal becomes processed into
an electric signal in these sensilla: reception of the stimulus in the external parts of
the sensillum, transmission by the distal and middle regions of the outer dendritic
segment, mechanical amplification by the proximal region, and finally transduction of
the mechanical signal into an electric signal at the junction of the outer and inner dendritic
segments (see figs. 7.12, 7.13 in volume 1 of the present series: Hallberg & Chaigneau,
2004).
Chemoreceptors. – Compared with mechanoreceptors, the diversity of chemoreceptors (fig. 54.28S-U) is generally greater on the flagella of the antennulae in Mysida and
Lophogastrida (Juberthie-Jupeau & Crouau, 1977; Crouau, 1978a; Hallberg et al., 1992;
Johansson & Hallberg, 1992; Johansson et al., 1996). Juberthie-Jupeau & Crouau (1977)
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Fig. 54.28. Sensory setae in Mysida (A-S) and Lophogastrida (T, U). A-E, Interpretative scheme for
various sensory setae of the mysid Praunus flexuosus (O. F. Müller, 1776), using terminology of
Debaisieux (1949a). A, armed seta from sympod of antennula; B, armed seta dorsally on uropods;
C, sensory seta from statocyst; D, unarmed simple seta from appendix masculina of antennula; E,
olfactory seta; F-R, twelve types of setae from mouthparts and thoracic endopods of the tropical
subterranean, anophthalmic mysid Antromysis juberthiei Băcescu & Orghidan, 1977: in terminology
of Crouau (1989) these are plumose (F-H), pappose (J), small (K), pushing (L), and serrulate (M-R)
setae, respectively; S, aesthetasc (ae) and companion setae on antennula of Antromysis juberthiei;
T, U, setae on outer antennular flagellum of female (T) and male (U) Lophogaster typicus M. Sars,
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gave a detailed description of an antennular aesthetasc of Antromysis juberthiei, including
a schematic representation, which is reproduced in fig. 7.19 in volume 1 of the present
series (Hallberg & Chaigneau, 2004). During the moulting process of antennal sensilla in
the mysid Neomysis integer, the dendritic segments of the old sensory cells remain continuous with the dendritic outer segments of the new sensillum; ensuring that the sensitivity
of the receptors is maintained until ecdysis (Guse, 1980). Olfactory abilities are important
in the search for food, detection of predators, recognition of conspecifics, and many other
purposes.
Male-specific sets of setae. – Clearly for the detection and pursuit of potential mating
partners (Guse, 1983b; Hallberg et al., 1992; Johansson & Hallberg, 1992; Johansson
et al., 1996), the males of most Mysidae have a dense brush of setae on the appendix
masculina (fig. 54.12E, G), which emerges ventrally from the terminal segment of the
antennular peduncle. Rarely, e.g., in certain species of Boreomysis and Heteromysis, this
brush may arise (almost) directly from the terminal segment of the peduncle. In each
mode of setae implantation, the sensilla-bearing parts are moveable by a special muscular
arrangement (Johansson & Hallberg, 1992). The Petalophthalmidae and certain Mysidae
lack an appendix masculina; instead their males show a thickened basal portion of the outer
antennular flagellum furnished with dense rows of aesthetascs. Some Boreomysinae
and Gastrosaccinae (fig. 54.12G) have an appendix masculina together with a modified
outer flagellum of the male antennula. In certain Mysidae, a basally thickened, setose
outer flagellum is present in both sexes, but usually less strongly in females. Lowry
(1986) emphasized the particular modifications of the outer antennular flagella as a distinct
sensory organ, termed ‘callynophore’ by him, found in many amphipods and in certain
mysids (fig. 54.12G), isopods, and decapods. He considered the function of these structures
to be detection of receptive females by chemoreception in those species in which they
occur only in reproductive males, or to be food detection where they occur in both sexes.
OTHER SENSORY ORGANS
The Petalophthalmidae genera Hansenomysis and Bacescomysis show a deep depression close to the base of the dorsal face of the proximal segment of the antennula. The
opening is partly covered by a fleshy lamella and was initially interpreted as a rudimentary
eye in these otherwise anophthalmic genera. Due to its position similar to that in decapods,
this depression has also been considered a statocyst, but there are neither any endogenous
nor exogenous static bodies. According to O. S. Tattersall (1961) the presence of small,
rounded, stainable areas point rather to a chemosensory function. In slightly more anterior
position on the same segment of the antennula, Mysimenzies (Mysidae: Erythropinae) has
1857, arrows indicate aesthetascs, arrowheads indicate companion setae (T) or typical male sensilla
(U). Abbreviations: ae, aesthetasc; at, axial tigelle; bfs, bifid seta; cm, chitinogenic matrix; coc,
connective cell; ec, ensheathing cell; sce, sensory cell; se, secretory cell; ss, simple seta; tf, tonic
fibrils. [A-E, after Debaisieux, 1949a; F-R, after Crouau, 1987; S, after Crouau, 1989, permission
granted by “© Canadian Science Publishing or its licensors”, Ottawa; T, U, after Johansson et al.,
1996; K, L, modified.]
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Fig. 54.29. Digestive system of the Mysidae (Mysida) (semi-schematic; A, B, F, simplified). A,
entire digestive tract of Mysis stenolepis S. I. Smith, 1873; B-E, fore- to midgut of Praunus flexuosus
(O. F. Müller, 1776), inner semi-transparent lateral view on right half of anterior region (B) and cross
sections (C-E) through posterior part of cardiac chamber (C), approximately mid-region of pyloric
chamber (D), and ventral lobe of hepatopancreas (E); F, G, Neomysis integer (Leach, 1814), midgut
glands in relation to foregut in lateral (F) and dorsal (G) view. Abbreviations: 1-5, numbers indicating
the series of lobe pairs of hepatopancreas; ab, alimentary belt; an, anus; cc, cardiac chamber (cardia);
cdp, cardiac dorsal piece (superomedianum); dc, dorsal caecum (dorsal diverticulum); dic, dorsolateral infolding of cardia; dip, dorso-lateral infolding of pylorus; dlt, dorso-lateral teeth; dpc, dorsal
pyloric chamber; fb, filtration belt; fc, food channel; fi, filtration channel; fn, funnel (lamina dorsalis
posterior); gm, gastric mill; he, hepatopancreas; hg, hindgut; lp, lateralia (lateral plates); lv, lamella
ventralis; mc, circular muscle; mg, midgut; ml, longitudinal muscle; ms, muscle; ocv, oesophageal
255
a sensory fossette, whereas its close relative Marumomysis merely has a setose elevation
(Băcescu, 1971a; Murano, 1999a). So far, no detailed knowledge is available about the
function of the various pores related to sense organs and to glands, present on eyestalks,
appendages, carapace, and body wall (see also above, ‘Integument and colour’).
Digestive system and digestion
History and gross structure. – The anatomy and structure of the digestive system (figs.
54.29, 54.30) were studied in various species of Lophogastrida (Siewing, 1953, 1956;
Oshel & Steele, 1988; De Jong, 1996; De Jong & B. Casanova, 1997; De Jong & J.-P.
Casanova, 1997; De Jong-Moreau et al., 2000; De Jong et al., 2002), Stygiomysida (Nath
& Pillai, 1972a), and Mysida (Van Beneden, 1861; G. O. Sars, 1867; Gelderd, 1909; Illig,
1912; Molloy, 1958; Haffer, 1965; Nath & Pillai, 1976; Friesen et al., 1986b; Storch, 1989;
Metillo & Ritz, 1994; Kobusch, 1998; De Jong-Moreau et al., 2000). All three orders are
covered by the studies of Kobusch (1999) and De Jong-Moreau & J.-P. Casanova (2001)
on the structure and evolution of the foregut. The early studies were greatly improved
upon the availability of electron microscopic techniques from the 1980s onwards. The
digestive system of these orders is of similar complexity as in decapods (Ceccaldi, 2006)
and like these shows three major parts (fig. 54.29A): the anterior intestine or foregut
(stomodaeum), consisting of oesophagus and stomach; the intermediate intestine or
midgut (mesenteron) composed of the midgut tube, hepatopancreas (midgut gland) and
potential additional midgut caeca; and the posterior intestine or hindgut (proctodaeum).
The foregut and hindgut are of ectodermal origin and entirely lined by cuticle, which is
renewed at each moult, whereas the midgut is of endodermal origin and without chitin
lining. The digestive tube is equipped with parietal circular and longitudinal muscles.
Some muscle bundles, particularly important at the height of the stomach, are connected
with the exoskeleton.
Foregut (figs. 54.29, 54.30). – The transversely cleft mouth is followed by a laterally
compressed, conical vestibular cavity, with the oesophagus departing from its bottom. The
oesophagus is nearly vertically (dorsally) directed in all Lophogastrida and Stygiomysida
so far examined (fig. 54.30A-C). It is forward inclined in most Mysida (fig. 54.29B),
but vertically directed in certain Mysidae (Mesopodopsis slabberi) and Petalophthalmidae
(Ceratomysis and Petalophthalmus). The ingestion of large food particles, already more
or less split by the mandibles and maxillae, is facilitated by peristaltic movements
of the oesophagus. According to Kobusch (1998) a total of up to four ventral, lateral,
and/or dorsal setose infoldings protrude into the oesophagus of the Mysida. These folds,
termed ‘cardio-oesophageal valves’, prevent the reflux of food into the oesophagus.
cardiac valve (valvula dorsalis oesophagi); oe, oesophagus; omg, outpocketing of the midgut; pc,
pyloric chamber (pylorus); ra, rectal ampoule; re, rectum; sfg, secondary filter groove; vcr, ventral
cardiac ridge (inferomedianum anterius); vpc, ventral pyloric chamber; vpr, ventral pyloric ridge
(inferomedianum posterius). [A, after Friesen et al., 1986b; B-E, after Gelderd, 1909; F, G, after
Kobusch, 1998; A, B, F, G, modified.]
256
257
There may be some discrepancies in definition with respect to De Jong-Moreau &
J.-P. Casanova (2001), who recognized only the dorsal cardio-oesophageal valve (fig.
54.29B) as being typical of all Mysidae, whereas they found only the ventral ones in
all Stygiomysida as well as in most Petalophthalmidae and Lophogastrida; those authors
found no valves in Petalophthalmus armiger (Petalophthalmidae). In certain species of
Lophogaster (Lophogastridae), the valves are also missing (De Jong, 1996) or reduced to
a wide, extremely flattened fold (Kobusch, 1999). The inner walls of the oesophagus are
always equipped with setae that face the stomach in order to promote the passage of food
and to impede reflux.
The oesophagus leads to the stomach, which in all taxa has a complex internal
structure formed by ridges and folds of different form and size, equipped with setae
and/or spines (fig. 54.30D-F). The stomach is stout and bulbous in most Mysida (fig.
54.29B), but extremely slender in certain Stygiomysida (Stygiomysidae; fig. 54.30B), and
of intermediate shape in the remaining Stygiomysida (Lepidomysidae; fig. 54.30A), in the
Lophogastrida (fig. 54.30C), and in certain Mysida (Mesopodopsis slabberi). The stomach
is functionally subdivided into an anterior cardiac chamber, a posterior pyloric chamber,
and the funnel (figs. 54.29B, 54.30A-C). Both chambers are in turn subdivided into a
dorsal region or ‘alimentary belt’ for storage, mechanical breakdown by mastication, and
transportation of the ingested material, and a ventral region or ‘filtration belt’ formed
by the primary cardiac filters and the more sophisticated secondary pyloric filters for
separation of fine particles and fluids. The dorsal alimentary belt of most Lophogastridae
(Ceratolepis, Chalaraspidum, and Lophogaster, but not so in Paralophogaster) is strongly
developed and forms a peculiar storage bag.
In the Mysida, the cardiac chamber is well separated from the pyloric chamber by
a dorsal gastric mill at its posterior end (fig. 54.29B). In contrast, the gastric mill is in
more anterior position within the cardiac chamber in Lophogastrida and Stygiomysida. In
this case, the two chambers are separated only by a pair of ventral cardio-pyloric valves.
In all three orders the gastric mill is generally composed of a median dorsal tooth (fig.
54.30E, F) and 1-2 pairs of lateral teeth (figs. 54.29C, 54.30C). Any of these teeth may be
reduced to simple folds or ridges depending on the taxon. The teeth, ridges, and folds may
show complex armatures of spinules and/or secondary teeth (Kobusch, 1998, 1999). The
lophogastrid genus Lophogaster has a modified gastric mill with the first pair of lateral
Fig. 54.30. Foregut of the Stygiomysida (A, B) and Lophogastrida (C-F); light microscopy photographs in lateral view (A-C) and SEM-micrographs of internal details (D-F). A-C, note the great
differences in longitudinal extension of cardiac (c), pyloric (p), and funnel (f) regions of foregut;
A, Spelaeomysis quinterensis (Villalobos, 1951); B, Stygiomysis major Bowman, 1976; C, Eucopia
sculpticauda Faxon, 1893; D, right side of ventral pyloric ridge in Eucopia australis Dana, 1852,
arrowheads indicate lateral grooves; E, antero-dorsal cardiac tooth in Gnathophausia ingens (Dohrn,
1870); F, detail of (E) showing spines of cardiac tooth. Abbreviations: 1, first lateral teeth; 2, second
lateral teeth; 3, antero-dorsal cardiac tooth; dpc, dorsal pyloric chamber; oe, oesophagus; piv, pylorointestinal valve; plse, lateral rows of plumose setae; vlpr, right ventro-lateral pyloric ridge; vpc, ventral pyloric chamber; vpr, ventral pyloric ridge. [A, B, after De Jong-Moreau & J.-P. Casanova, 2001;
C, D, after De Jong & B. Casanova, 1997; E, F, after De Jong & J.-P. Casanova, 1997, permission
granted by “© Canadian Science Publishing or its licensors”, Ottawa; A-D, modified.]
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teeth resembling internal mandibuliform appendages and with ventro-lateral cardiac plates
bearing spines reinforcing the gastric armature (De Jong, 1996). Within the lophogastrid
genus Eucopia, only Eucopia sculpticauda shows a dorsal tooth; the remaining species
conserve only a simple fold representing a rudiment of the basis of this tooth. Within the
Stygiomysida, Spelaeomysis shows a normal equipment consisting of a dorsal tooth and
a pair of lateral teeth; by contrast, the gastric mill of Stygiomysis is reduced to a vestigial
dorsal tooth in the anterior part of the extremely elongate cardiac chamber.
The primary cardiac filter is formed by a pair of ventro-lateral longitudinal folds
fringed by long setae; these folds cover a ventro-lateral furrow (filtration channel) on
both sides of a median ventral fold (fig. 54.29C, D). In Stygiomysis major (Stygiomysida),
however, the cardiac folds lack setae and, therefore, lack their filter function (De JongMoreau & J.-P. Casanova, 2001). The dorsal pyloric chamber is a simple canal for the
transport, through the funnel to the midgut, of the large particles and faecal material that
did not pass through the filters. The dorsal pyloric region is elongated by the tube-like
funnel (fig. 54.29B), which penetrates lengthwise into the lumen of the caudally adjacent
midgut. The funnel is in open connection with the interior of the midgut by a longitudinal
ventral fissure (Storch, 1989). As a derivate of the foregut, the funnel is of ectodermal
origin, even though penetrating inside the endodermal midgut.
A pair of longitudinal folds, fringed by long setae, separates the dorsal pyloric region
from the ventral one (fig. 54.29D). The secondary pyloric filter shows principally the same
configuration as the primary filter. A pair of ventro-lateral folds separates the ventro-lateral
furrows at each side from the median ventral part. The median ventral ridge represents the
most strongly projecting structure of the pyloric chamber. Laterally, it bears several rows
of setae, each row covering a furrow. These setae can form a very fine filtration net. In
the Stygiomysida and Mysida, there are usually 2-3 setal rows (fig. 54.29B) depending
on the taxon, but five rows are present in Ceratomysis (Mysida: Petalophthalmidae). The
Lophogastrida generally show greater numbers of rows, 4-5 in Lophogaster and 5-7 in
Eucopia (fig. 54.30D) and Gnathophausia. Intraspecific variations of these numbers are
correlated with differences in body size. The ventro-lateral folds bear numerous rows with
rasp-like setae. The ventral and ventro-lateral valves (fig. 54.30D) are prolonged towards
the intestine.
Midgut (fig. 54.29A, F, G). – Normally, the midgut starts dorsally at the posterior
pyloric chamber. However, its insertion is shifted ventrally in certain Lophogastrida
(Lophogastridae: Ceratolepis, Chalaraspidum, Lophogaster), probably in relation to the
large, dorsally overlying storage bag in these genera. The Mysida are equipped with a comparatively short, unpaired dorsal diverticulum or a dorsal caecum (fig. 54.29A, F, G), or
a pair of very small diverticula at the junction between stomach and midgut. The unpaired
dorsal diverticulum of the Stygiomysida species Spelaeomysis longipes is extremely long,
extending to the anterior end of the stomach (Nath & Pillai, 1976). According to Mauchline (1980), the dorsal diverticula secrete the peritrophic membrane into the intestine.
However, Friesen et al. (1986b) interpreted the potential function of the dorsal caecum in
the mysid Mysis stenolepis more cautiously: “. . . the zymogene-like granules and large
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amounts of rough endoplasmic reticulum suggest a secretory role”. No such diverticula
or caeca are present in Lophogastrida (De Jong-Moreau et al., 2000). Posterior midgut
caeca are so far known only from the freshwater subterranean Stygiomysida Spelaeomysis
longipes and are used for calcium storage (see below, ‘Moulting’).
The hepatopancreatic ducts join the midgut at the level of the ventro-lateral folds via
a pair of latero-posterior orifices (fig. 54.29F). The Mysida generally have five pairs of
hepatic caeca within the thorax. Two among the five pairs are very short and directed
obliquely upwards, whereas the remaining three are posteriorly directed along the intestine
(fig. 54.29A, F, G). Among these last three pairs, the upper and the lower pairs extend
along most of the thorax; the median pair is shorter and closest to the intestine walls. The
stygiomysid Spelaeomysis longipes has a total of only three pairs, of which the shortest
one turns posteriorly and the two longer pairs extend dorsally along the intestine (Nath &
Pillai, 1972a). In the Lophogastrida, the hepatopancreas consists of only two large and
irregularly shaped caeca, one on each side of the intestine (De Jong-Moreau et al., 2000).
After approaching the sternites, the intestine runs through the dorsal lacuna of the pleon.
Friesen et al. (1986b) studied the ultrastructure of the intestine and the hepatic caeca
of Mysis stenolepis. These authors reported the main cell types known from decapods
(Ceccaldi, 2006): E- or S-cells (embryonic or stem cells, respectively), F (fibrillary
cells; supply enzymes for extracellular digestion), B (blister-like cells, implicated in
intracellular digestion), and R (resorptive cells; for lipoprotein metabolism). De JongMoreau et al. (2000) studied two species of Lophogastrida plus three species of Mysida
and found marked differences in hepatopancreas structure between the two orders. They
identified only B- and R-cells but no F-cells in their material, and doubted that the “F-cells”
claimed by Friesen et al. (1986b) for Mysis stenolepis were true F-cells. The posterior part
of the midgut forms an ampoule-like structure (fig. 54.29A).
Hindgut (fig. 54.29A). – The rectum is very short and restricted to the sixth pleonite;
it is lined by a chitinous cuticle. The anus opens ventrally at the base of the telson (fig.
54.22F).
Digestion. – The first phase of digestion takes place at the level of the external
mouthparts, mainly by breaking the food in pieces and grinding it. In Lophogaster typicus,
secretions of the labrum probably help to coat and digest the food (De Jong et al.,
2002). The second main phase takes place in the stomach. This involves (1) mechanical
digestion by mastication, (2) chemical digestion by digestive enzymes, (3) separation of
fluids and fine particles from large particles by filters, and (4) transport of fluids and
fine particles to the hepatopancreas and of large particles to the intestine for subsequent
defecation through the rectum. In Lophogaster, the reduced size of the intestine and its
ventral junction with the stomach at the secondary filter do not permit the transport of
large particles via the intestine. Large, non-reducible particles are probably regurgitated in
Lophogaster, where this phenomenon is additionally facilitated by the (near) absence of
the cardio-oesophageal valve.
The final phases of the digestive cycle take place in the hepatic caeca or hepatopancreas, namely (1) an extra- and intracellular enzymatic digestion of the pyloric filtrate,
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and (2) the production of digestive enzymes for the phases of digestion in the stomach.
In addition, peculiar spines, each with an apical pore, are present in the lophogastrid Eucopia sculpticauda on each of the first lateral teeth of the gastric mill. This suggests a
secretory role of the subjacent stomachal epithelium (De Jong & B. Casanova, 1997).
Zimmer (1932) and Molloy (1958) observed antiperistalsis, which may be continuous
or may vary with gut content, depending on species in Mysida. Fox (1952) observed anal
and oral intake of water in various crustaceans, including the mysids Hemimysis lamornae
and Siriella armata. He concluded that oral and anal drinking is needed to stretch the gut
wall muscles until they can contract by antiperistalsis.
Circulatory system
The circulatory system (fig. 54.31A, C-E) was studied in several species of Mysida
by Van Beneden (1861), G. O. Sars (1867), and particularly by Delage (1883), Claus
(1876, 1884), and Wirkner & Richter (2007). Mayrat (1956b) re-described the cephalic
aorta and its branches. Gadzikiewicz (1905) provided several histological details of the
heart. Many characters of the circulatory system described by Siewing (1953, 1956) for
the Lophogastrida species Eucopia sculpticauda and Eucopia unguiculata are reminiscent
of those in Mysida. A slightly more simple vascular system was found by Belman &
Childress (1976) in the lophogastrid Gnathophausia ingens. Major progress was achieved
by Wirkner & Richter (2007), who applied the corrosion casting method in combination
with computer-aided 3D reconstruction on three species of mysids and on the lophogastrid
Lophogaster typicus. So far no details are available about the circulatory system of the
Stygiomysida. A detailed overview of crustacean circulatory systems is available in the
second volume of the present series (Mayrat et al., 2006).
C IRCULATORY SYSTEM OF THE M YSIDA
General features of the circulatory system (fig. 54.31C-E). – According to Delage
(1883), Mayrat (1956b), and Wirkner & Richter (2007), this system is characterized by a
contractile tubular heart that extends dorsally from thoracomere 1 to at least thoracomere
7, in part back to the anterior part of pleomere 1. It shows two pairs of ostia within the
inflated median part, close to the border of thoracomeres 3 and 4: the posterior pair is
more ventrally located than the anterior one (fig. 54.31D). Due to its uppermost position
within the thorax, the heart is, on its ventral face, connected with the underlying dorsal
diaphragm. Its innervation was studied by Alexandrowicz (1955) in Praunus flexuosus.
There are at least three systems of nervous elements: a local ganglion system with its cell
bodies on the dorsal wall and its axons innervating muscle fibres; a pair of cardiac nerves
connecting with the central nervous system; finally, a particular innervation in the valves
of the arteries leading away from the heart.
Anterior arteries (fig. 54.31C). – The anterior aorta, equipped with a valve near its
origin, lengthens the heart anteriorly. It widens to a myoarterial formation (accessory
pumping structure) attached to the posterior wall of the stomach, continues over the
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stomach, and then bends ventrally at the anterior margin of the stomach, where it gives off a
sac-like widening. Then it continues anteriorly as an ophthalmic artery, which bifurcates
to the eyes. Ventrally it emits a small upper cephalic artery plus a pair of cephalic arteries
that ramify in the brain and anastomose in a plexus from which the antennular arteries
depart. Here, the aorta shows a second myoarterial formation and emits a pair of antennal
arteries and finally opens into the labral haemocoel. In its anterior region, the heart emits
a pair of backwards-curved cardiac (hepatic) arteries that supply musculature, ovaries,
and midgut glands (hepatopancreas). More caudally and ventrally, three small, unpaired
arteries penetrate the dorsal diaphragm and branch into the viscera of the body cavity.
Descending artery (fig. 54.31C). – An additional, very important artery originates
at the posterior ventral region of the heart. This is the sternal artery or descending
artery (equipped with valves), which descends almost vertically in the posterior part of
the seventh somite, passes aside of the intestine, then turns anteriorly along the sternal
walls and the nervous chain up to the mouth area. Before bending anteriorly, the sternal
artery emits, depending on the taxon, 1-2 branches which supply the appendages of the
2-3 posterior thoracic somites with lateral arteries, while the main trunk, which crosses the
ventral nervous chain, supplies the appendages of the more anterior somites at least up to
the maxillae. The sternal artery also supplies the nervous chain and the sternal portions of
the thorax.
Abdominal artery (fig. 54.31C). – The heart is prolonged posteriorly by an abdominal
artery. The latter is also equipped with valves at its point of origin, runs dorsally along
the digestive tube, sends ventrally an arteriole to the ultimate thoracic somite and to each
of the five anterior pleonites and their appendages, as well as a lateral arteriole to each
of these latter. The abdominal artery bifurcates upon reaching the ultimate pleonite: one
branch ends in the telson; the other, smaller one turns anteriorly after having sent arterioles
into the rami of the uropods.
Lacunae and pericardium (fig. 54.31D, E). – When leaving the arteries, the blood
drains into the lacunae, of which the principal one is located between the thoracic viscera.
Two other important lacunae extend into the pleon: one into the medio-dorsal flanks of
the intestine, the other into the ventral region accompanying the nervous chain. The blood
that circulated in the secondary lacunae of the head and its appendages as well as the
eyes, returns in part into the thoracic lacunae, in part into the lateral duplicatures of the
carapace, where it proceeds along the lower (= inner) margin of the carapace (fig. 54.31D).
The blood coming from the lacunae of the pleon returns partly into the pericardium (fig.
54.31E), partly into the large thoracic lacuna. From the latter, some of the sanguine flux
enters the lacunae of the appendages, the remainder joins the torrent coming from the base
of the eyes, and flows also to the lower margin of the carapace. All the blood passing
through the respiratory lining in the duplicature of the carapace flows up to the dorsal
region of the carapace, and flows into the pericardium through a short canal. Finally, the
blood circulating in the seven posterior pairs of thoracic appendages also returns to the
pericardium through seven pairs of podo-pericardial sinuses (fig. 54.31E).
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Fig. 54.31. Circulatory and respiratory systems of the Lophogastrida (A, B) and Mysida (C-G). A,
C, interpretative schemes for heart and arterial system in Lophogaster typicus M. Sars, 1857 (A) and
Boreomysis arctica (Krøyer, 1861) (C); B, series of branchiae on thoracopods 2-8 in Gnathophausia
longispina G. O. Sars, 1883, carapace removed, lateral; D, E, semi-schematic presentations of afferent lacunae and sinuses in Praunus flexuosus (O. F. Müller, 1776) showing lacunae of respiratory
carapace (D, lateral) and vessels returning from thoracopods (E, dorsal, overlying tissues removed),
arrows indicate direction of flow; F, natatory and feeding currents, also supporting respiration,
produced by a freely swimming Hemimysis lamornae (Couch, 1856); G, same species as before,
arrows show movements of right epipod in respiratory chamber, lateral. Abbreviations: a1a, first
antennal artery; a2a, second antennal artery; aad, anterior stomach aorta dilation; ala, anterior lateral
artery; ao, anterior aorta; apl1-apl5, arteries for the pleopods 1-5; bra, brain artery; ca, carapace;
cca, cardiac artery; cpv2-cpv8, cruro-pericardial vessels from thoracopods 2-8; dea, descending
artery; ep, epipod; ex, base of thoracic exopod; ha, heart; ic, insertion of the carapace; lb, labrum;
lo, luminescent organ; mafa-mafc, myoarterial formations a-c; mav, marginal afferent vessel of the
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C IRCULATORY SYSTEM OF THE L OPHOGASTRIDA
This system (fig. 54.31A) differs from that of the Mysida essentially by an additional (third), much more anterior pair of ostia, and by a greater number and different
arrangement of cardiac arteries, whereby the posterior-most artery extends into the first
pleomere. The antennae are supplied by a pair of anterior lateral arteries that branch as
the first pair of arteries directly off the heart. The podo-pericardial sinuses of thoracopods
2-7 fuse with sinuses from the respective gills and then extend to the pericardium (Wirkner
& Richter, 2007).
Respiratory system
Lophogastrida (fig. 54.31B). – Gas exchange takes place mainly in the gills, which
arise as epipods from the coxae of thoracopods 2-7. The importance of the gills for respiration is underlined by their strong development in Eucopia crassicornis, described from
oxygen-poor waters in the Canal of Mozambique (J.-P. Casanova, 1997). Gills are always
present irrespective of body size and cuticle thickness, as exemplified by comparison between the ‘giant’ Gnathophausia and the small Paralophogaster. The respiratory current
is driven by the movements of the exopods of the natatory thoracopods and by the back
and forth movements of the epipod of the first thoracic appendages. According to Childress (1971), in Gnathophausia ingens the exopod of the maxilla also contributes by
ventilation movements.
Mysida (fig. 54.31D, F, G). – Gas exchange takes place mainly through the inner face
of the carapace duplicature according to the classical interpretation (e.g., Delage, 1883;
Tattersall & Tattersall, 1951; Kobusch, 1999). This conclusion is essentially based on
anatomical evidence, particularly on the characteristic network of haemolymph channels
below the lining of the inner carapace wall (fig. 54.31D). In the space between the
duplicature and the lateral wall of the thorax, the water driven by the beats of the epipod
(fig. 54.31G) pertaining to the first thoracopod, circulates quite busily (Cannon & Manton,
1927a; Attramadal, 1981). The reduction of the respiratory carapace surface in the cavedwelling Palaumysis is interpreted above (under ‘Carapace’) as a consequence of dwarfing.
Due to the absence of respiratory tissue it appears unlikely that the laminar (e.g., in
Mysinae, Leptomysinae) or curled (in males of most Siriellinae) pseudobranchial lobes
on the basis of the endopods of the pleopods (fig. 54.21G) have some respiratory function
in the Mysidae.
Stygiomysida. – This order shares the respiratory carapace with the Mysida (Wägele,
1994; Kobusch, 1999). Almost all species of Stygiomysida show a subterranean mode
carapace; mx1, maxillula; mx2, maxilla; oa, optical artery; os, ostium; pao, posterior aorta; per,
pericard; pl1, first pleopod; plm, palpus mandibularis; rc, respiratory carapace; si, sinus; tn1-tn2,
thoracic endopods 1, 2; trm, mandibular trunk; tx2-tx8, thoracic exopods 2-8; uca, unpaired cardiac
artery. [A, C, after Wirkner & Richter, 2007 (figures modified and kindly made available by C.
Wirkner); B, after Sars, 1885a; D, E, after Delage, 1883; F, G, after Cannon & Manton, 1927a; A,
C-G, modified.]
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of life. Among the two genera constituting this order, only Stygiomysis has a caudally
strongly shortened carapace with reduced surface of the carapace cavity (figs. 54.3A,
54.7J; cf. above, ‘Carapace’). The species of this genus are comparatively large (5-21 mm)
and at least Stygiomysis hydruntina is capable of performing relatively quick movements
(Inguscio, 1998). Therefore, neither dwarfing nor a strongly reduced basic metabolism are
available as potential explanations for reduction of the respiratory carapace.
Reproductive system
As in most Malacostraca, the Lophogastrida, Stygiomysida, and Mysida are gonochoristic, apart from rare effects of intersexuality. The secondary sexual characteristics are
acquired successively upon a number of moults. Unlike males, the females of certain taxa
may adopt a resting stage at the end of the reproductive period (see below, ‘Adjustment of
reproductive parameters’). Hermaphroditism and reversal of sex were never observed, not
counting partial reversal undergone by intersexes (see below, ‘Intersexuality’).
Female genital apparatus. – According to G. O. Sars (1867) and Holmquist (1959),
the female genital apparatus (fig. 54.32) of the mysid Mysis relicta contains two parallel,
joined cylindrical tubes, connected by a sacciform median bridge representing a true
ovary. This portion of the apparatus is located between the digestive tube and the bottom
of the pericardium. It extends from the region of the stomach to the posterior margin of
the second pleonite (J.-P. Casanova, 1977) in mature females of the lophogastrid Eucopia
unguiculata, and to the margin of only the first pleonite (Mauchline, 1980) in the mysid
Praunus flexuosus. A quite large oviduct departs from the posterior portion of each tube.
The only process occurring inside the oviduct is oocyte growth. According to Nair (1939),
the mysid Mesopodopsis orientalis shows two pairs of parallel, longitudinal, differently
developed tubes. The ovary opens on the right and on the left into a first pair of shorter
thin tubes which lead with their anterior end into a second pair of longer and thicker tubes.
The swollen terminal portion of the oviducts is glandular, with secretion taking place
shortly before oviposition. Observed through the transparent ovarian tubes, the yolk of
the oocytes may appear colourless or quite often vividly yellow, red, green, blue, or violet.
As in all Malacostraca, the female genital orifice is located at the base of the sixth pair
of thoracic appendages. The eggs are relatively large (see ‘Egg size’ below) and have a
distinctly eccentric nucleus. Fertilization takes place after oviposition in the marsupium.
So far no receptacula seminis have been found in any females of the three orders.
Male genital apparatus (fig. 54.33). – The male genital apparatus was first described
by G. O. Sars (1867) for the mysids Mysis relicta and Praunus inermis as a horseshoe-like
tube bearing about twenty testicular lobes, with two deferent canals departing from the
ends of that tube. Later observations showed that this concept was erroneous. Labat (1961)
observed for Praunus flexuosus that two independent, parallel, elongated testes are located
in the medio-dorsal anterior region of the thorax, between the heart and the hepatic lobes,
and behind the stomach. Along each testis, 5-6 efferent canals end in large cysts, most of
the latter in lateral arrangement, only the anterior pair in frontal position. These cysts were
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Fig. 54.32. Female genital apparatus of the Mysida. A, its position in body of Praunus flexuosus
(O. F. Müller, 1776), lateral view; B, ovary and oviducts in young female Mysis relicta Lovén,
1862, dorsal view; C, ovary of Mesopodopsis orientalis (W. M. Tattersall, 1908), ventral face;
D, transversal section through the latter, at connection with the two pairs of longitudinal tubes.
Abbreviations: ha, heart; he, hepatopancreas; in, intestine; od, oviduct; ot, ovarian tubes; ovb, ovarian
bridge; pnl, postnauplioid larvae in marsupium (highly schematic); sto, stomach. [A, modified after
Mauchline, 1980; B, after G. O. Sars, 1867; C, D, after Nair, 1939.]
previously considered as true testes. They themselves communicate with two large tubes,
which are independent of each other and located dorsally with respect to the testes. These
tubes should be precisely named seminal vesicles, at least for their anterior, blind-ending
parts, which are joined, curved down to the ventral parts of the body, and show a glandular
epithelium that secretes mucus and other substances. Each seminal vesicle is prolonged
posteriorly by a deferent canal that swells, forming an ampulla prior to ending at the male
genital orifice close to the tip of the respective penis.
The spermatogonia grow in the swellings of the testicular chain and then pass through
the cysts, where they undergo meiotic divisions and spermatogenesis. In each cyst, all
elements are in the same meiotic state as found in the symmetrical cyst. In Praunus
flexuosus, the ripe spermatozoa are released into the seminal vesicles in groups of 3,
4, or 5 (Labat, 1962). Each group is surrounded by the mucous substance secreted by the
glandular epithelium of the seminal vesicle. This forms a type of spermatophore. The
spermatophores accumulate in the deferent canals of the terminal ampulla. Leptomysis
lingvura produces a much larger spermatophore: a sack-like, distally narrowing, sticky,
soft membrane containing a large sperm mass (fig. 54.36G; Wittmann, 1982). The structure
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Fig. 54.33. Male genital apparatus of the Mysida (A-G) and Stygiomysida (H, J). A, its position
in body of Praunus flexuosus (O. F. Müller, 1776), lateral view; B, genital apparatus of same
species in dorsal view, object slightly expanded, only beginning of anterior portion of fine testicular
canals shown; C, anterior portion of (B) in lateral view; D, anterior portion of (B) in ventral
view; E, section through anterior end of seminal vesicle of Praunus flexuosus; F, spermatozoon
of Mysis oculata (Fabricius, 1780); G, anterior portion of spermatozoon of Praunus inermis
(Rathke, 1843) showing insertion of tail, schematic; H, position of genital apparatus in Spelaeomysis
longipes (Pillai & Mariamma, 1964); J, androgenic gland with juxtaposed structures in Spelaeomysis
longipes. Abbreviations: acm, anterior coxal muscle; ag, androgenic gland; cl, coxal lobe; de,
ductus ejaculatorius (ejaculatory canal); ha, heart; he, hepatopancreas; in, intestine; nu, nucleus;
pcm, posterior coxal muscle; pe, penis; sh, shaft; smv, seminal vesicle; sp, spermatidic pouch; sto,
stomach; ta, tail; tst, testis; vd, vas deferens. [A, after Mauchline, 1980; B-E, after Labat, 1961;
F, after Retzius, 1909; G, after Fain-Maurel et al., 1975, permission granted by Elsevier B.V.,
Amsterdam; H, J, after Nath et al., 1972b; A, F, H, J, modified.]
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of the spermatozoa of the Mysida corresponds to that of the Amphipoda and Isopoda.
They are whip-like, oblong, and immotile, composed of a long and thin shaft with an
even longer, transversely striated tail (flagellum) (fig. 54.33F; Fain-Maurel et al., 1975;
Wittmann, 1982). They are 0.5-1.3 mm long, including the long flagellum, and thus may
be visible already with low-power microscopy through the wall of the ductus ejaculatorius
(Wittmann, 2013b).
In the mysids Praunus flexuosus and Paramysis nouveli (cf. Juchault, 1963; Meusy,
1963), a pair of androgenic glands is present in the last thoracomere, close to the end
of the external wall of the deferent canals. An identical arrangement can be found in the
androgenic glands of the cavernicolous Lepidomysidae Spelaeomysis longipes, but their
structure appears to indicate a weaker secretory activity (fig. 54.33J; Nath et al., 1972b).
Finally, mention should be made of the valuable survey by Kasaoka (1974) on the
male genital apparatus in the mysids Archaeomysis grebnitzkii and Neomysis awatschensis.
The structure of the external male genitalia is treated above in the section ‘Thoracic
appendages’.
Excretory system and excretion
Excretion takes place in segmental glands (fig. 54.34). All Lophogastrida and Mysida
have a pair of antennal glands consisting of a sacculus and a more or less long and
irregular secretory canal that swells into a vesicle at its terminal portion. Only the sacculus
located in the praecoxa of the antenna, shows excretory function. The entire gland is of
mesodermal origin, except for the ectodermal nephrostome located on the latero-ventral
face of the antennal coxa (Grobben, 1881; Cannon & Manton, 1927b; Vogt, 1932, 1933,
1935a).
Mysida (fig. 54.34A, B). – Tchindonova (1981) found hypertrophic antennal glands
in eight genera of Erythropinae (Mysida) characterized by eye plates with reduced visual
elements. In contrast, normally developed antennal glands are present in genera with welldeveloped eyes. Vogt (1932) found mesodermal cells, termed by him ‘athrocytes’ (fig.
54.34A; i.e., not ‘arthrocytes’), at the base of the thoracopods in Mysida and concluded
that they possibly represent storage cells and do not contribute to excretion. Without
indication of details or literature sources, Tattersall & Tattersall (1951) did not exclude
a certain contribution by these cells to excretion. Studies on other crustacean groups by
Hosfeld & Schminke (1997) showed that such cells possibly represent podocytes, i.e.,
typical excretory cells.
Lophogastrida (fig. 54.34C). – Antennal glands as well as maxillary glands are
present in this order. Both types of excretory organs have principally the same structure. In
Lophogaster, the excretory canal is straight, with the nephrostome placed at the end of the
first segment of the maxillae (Cannon & Manton, 1927b). Such glands were also described
for Eucopia by Siewing (1956). According to Calman (1909) the maxillary glands produce
a bioluminescent secretion in Gnathophausiidae (luminescent organs in figs. 54.10O,
54.31B). Frank et al. (1984) reported that Gnathophausia ingens loses its luminescent
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Fig. 54.34. Excretory system in Mysida (A, B) and Lophogastrida (C). A, antennal gland and series
of athrocytes in cephalothorax of Praunus flexuosus (O. F. Müller, 1776); B, left antennal gland in
Mysis relicta Lovén, 1862; C, reconstruction of excretory organs on left side of Lophogaster typicus
M. Sars, 1857. Abbreviations: a2, antenna; ang, antennal gland; anp, antennal nephroporus; ath,
athrocytes; beb, blind ending bladder; db, dorsal bladder; ey, eye; he, hepatopancreas; md, mandible;
mec, mesodermal cells; mx2, maxilla; mxg, maxillary gland; sa, sacculus (end sac) of the antennal
gland; sm, sacculus (end sac) of the maxillary gland; sto, stomach; tx2-tx8, thoracic exopods 2-8.
[A, after Vogt, 1932; B, after Vogt, 1933; C, after Cannon & Manton, 1927b; A-C, modified.]
capacity in the laboratory when fed a diet restricted to tissues from non-bioluminescent
animals and rapidly regains this capacity after ingesting certain luminescent prey. This
would indicate that luminescence would not originate from the species itself, but rather be
dependent upon components of its food.
Endocrine organs
Endocrine organs of the eyestalk. – In the Mysida and Lophogastrida, neurohormones involved in the endocrine control of moulting and reproduction are produced in
the eyestalks, as in Decapoda, rather than more directly in the brain as in Amphipoda and
Isopoda. The sinus gland in the eyestalk and the frontal organ in the frontal plate were
already described above, together with the nervous system of the lophogastrid Eucopia.
The sinus gland was localized and described in detail within the eyestalk (fig. 54.24D) of
the Mysida genera Mysis, Paramysis, and Siriella by Gabe (1953), Hogstad (1969), and
Cuzin-Roudy & Saleuddin (1985). These later authors described the “medulla externa –
medulla interna X-organ (ME-MI X-organ)” and “medulla terminalis X-organ (MT Xorgan)” as neurosecretory and neurohaemal organs involved in moulting and reproduction. Cauterization of the MI-ME X-organ showed no effect when performed after apolysis
(segregation of the old cuticle), but inhibited moulting when performed before apolysis
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(Cuzin-Roudy & Saleuddin, 1985) in both sexes of Siriella armata. In the latter case, secondary vitellogenesis ceased and the breeding females could not stop incubation — and
their marsupial young could not perform the second larval moult. Kulakovskii (1969, 1971)
described neurosecretory cells of the eyestalk involved in the hormonal control of the chromatophores in Mysis oculata. Previously assumed neurosecretory and neurohaemal functions of the organ of Bellonci (SPX-organ) in the eyestalk appear currently doubtful (see
above, ‘Nervous system’).
Y -organ. – The “lateral organ” described by Vogt (1935b) for the first maxillary segment of the mysid Gastrosaccus spinifer was listed by Charmantier-Daures & Charmantier
(2006) as a Y-organ. Gabe (1953, 1956) identified a Y-organ in the mysid genera Siriella,
Praunus, and Paramysis, where it is located in the second maxillary segment and innervated by the sub-oesophageal ganglion. It is comparable to the Y-organ of the decapod
crustaceans (Lachaise et al., 1993) and to the moulting glands of insects (Covi et al., 2012),
and it probably plays a role for the secretion of the moulting hormone.
REPRODUCTION AND SEXUALITY
Sexual dimorphism
Beyond the gonads or primary sex organs (cf. above, ‘Reproductive system’) and the
accessory sex organs (penes and oostegites; cf. ‘Thoracic appendages’) all taxa show at
least some secondary sexual traits, which together constitute a generally strong sexual
dimorphism.
Lophogastrida. – In this order, sternal projections are generally present on the
posterior thoracomeres of juveniles. These projections become more conspicuous with
increasing body length, and form one — sometimes two — strong peaks in adult males
(fig. 54.35A). In contrast, these projections are reduced in females with approaching sexual
maturity, at the same time when granular areas appear at their position. These areas bear
long barbed setae (fig. 54.35B) penetrating the space between eggs (embryos) or larvae
(Fage, 1936, 1940, 1941, 1942; Nouvel, 1942a, 1943). In Eucopia, sexual dimorphisms
may concern the antennular peduncles, the antennal scales (also in Gnathophausia), and
in a very constant manner the pleopods, the thoracic exopods, and the gills. The latter are
more strongly developed in the males (fig. 54.35L) than in the females (fig. 54.35K). In the
Lophogastrida, the male-specific sensilla appear to be generally less restricted to certain
portions of the antennula than in the Mysida (Johansson et al., 1996): All along the outer
antennular flagellum of male Lophogaster typicus, there are male-specific aesthetascs (fig.
54.28U) in addition to those also present in females (fig. 54.28T). The pleopods of the
Lophogastrida are well developed and natatory, not or only weakly modified in both sexes
(see above, ‘Pleopods’).
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Stygiomysida. – The exopod of the second male pleopod is slightly modified and
generally shows more setae, but has always one segment less compared to that of adult
females (fig. 54.17H versus 54.17J): in Spelaeomysis the male shows only three segments
instead of four (Pesce, 1976a), and in Stygiomysis it shows only two instead of three
segments (Bowman, 1976).
Mysida. – Diverse sexual differences, sometimes quite particular ones, may concern
the formation of the frontal plate, antennulae, antennal scale, certain thoracic and pleonal
appendages, as well as the armature of telson and uropods, particularly the form of their
spines. In certain cases the pigmentation also varies according to sex and state of sexual
maturity.
The males of most taxa have a stronger, stouter antennula with greater diversity
and numbers of sensory setae. In adult males of the family Mysidae, the appendix
masculina (see above, ‘Antennula’), less frequently termed ‘processus masculinus’ or
‘lobus masculinus’, is covered by a dense brush of sensory setae (fig. 54.12C, E, G).
The setae are lacking or are very sparse in subadult males. Their full presence marks the
attainment of the adult stage. The male lobe varies greatly between the taxa. It is very long
in the Siriellinae, but may be reduced to a small setose ridge or hump in other subfamilies.
In certain Boreomysinae and Heteromysinae it represents only a brush of setae ventrally
on the terminal segment of the antennular peduncle.
As a diagnostic feature of the subfamily Gastrosaccinae (Mysida: Mysidae), the first
pleomere of the females shows pleural plates (fig. 54.5F) supporting the marsupium.
Such plates are generally absent in males; if present, they are smaller than in females.
Curiously, there is also an inverse case characteristic at subfamily level within the Mysidae:
in all species of Rhopalophthalminae, the males show a pair of well-projecting, rounded
pleural plates (arrow in fig. 54.4C) from the first pleomere, whereas such plates are
completely absent in the females (O. S. Tattersall, 1957; Panampunnayil & Biju, 2006;
Vilas-Fernández et al., 2008; Hanamura et al., 2011). The proximity of these plates to the
specially modified genital structures in males of this subfamily suggest some unknown
role in mating (Wittmann, 2013b).
Compared to the Lophogastrida, sternal projections from the thoracomeres are much
less common and are scattered over various taxa in the Mysida. In certain species of
Heteromysis, such projections are well developed and covered by spines or teeth (fig.
54.15N) in males, whereas they are absent or small, hump-like (fig. 54.15M), never with
spines or teeth, in females (Nouvel, 1940; Băcescu, 1968a; Wittmann, 2000, 2008). Many
Atlantic and Pontomediterranean species of Paramysis show lobe-like to long sickleshaped projections in adult males (fig. 54.35D, E). These projections are shorter and more
hump-like in juveniles of both sexes (fig. 54.35C). In analogy to the Lophogastrida, such
projections are missing in adult females (Labat, 1953; Wittmann & Ariani, 2011).
The thoracic endopods are often more strongly developed and may bear different
sets of setae in the males: in Heteromysis and closely related genera, the ‘tarsus’ (i.e.,
carpopropodus plus dactylus) of the third male endopod (fig. 54.35G) is typically stouter
and more prehensile than in the females (fig. 54.35F). Depending on the species of
Surinamysis, at least some among endopods 5-8 are longer, with particular sets of setae
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Fig. 54.35. Sexual dimorphism of thoracic sternites and thoracopods in Lophogastrida (A, B, K,
L) and Mysida (C-J). A, B, equipment of some thoracic sternites in Lophogaster typicus M. Sars,
1857, for male (A) in lateral view and for female (B) in frontal view; C-E, series of thoracic
sternites 1-8 in lateral view, for juvenile (C) Paramysis pontica Băcescu, 1940, an adult male (D)
of same species, and an adult male (E) of Paramysis bakuensis G. O. Sars, 1895; F, G, third thoracic
endopods in female (F, frontal aspect) versus slightly smaller male (G, caudal aspect) Heteromysis
wirtzi Wittmann, 2008; H, J, seventh thoracic endopods in female (H) versus male (J) Surinamysis
merista (Bowman, 1980); K, L, size of gills and exopods of seventh thoracopods in female (K) versus
male (L) Eucopia unguiculata (Willemoës-Suhm, 1875). Abbreviations: ba, basis; br, branchiae; cr,
carpus; cx, coxa; end, endopod; ex, exopod; sp2-sp6, sternal processes after thoracomeres 2-6; ts1ts8, thoracic sternites 1-8. [A, B, after Fage, 1942; C-E, after Wittmann & Ariani, 2011; F, G, after
Wittmann, 2008; H, J, after Bowman, 1980; K, L, after Nouvel, 1942a; A-L, modified.]
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or with other modifications in males (fig. 54.35J) compared to those of females (fig.
54.35H). For female-specific structures associated with the marsupium see above, under
‘Oostegites’.
The male pleopods (fig. 54.21) are well developed or generally less reduced compared
to those of the females. Among the ten subfamilies of the Mysidae, strong modifications
mark the male pleopods of the Rhopalophthalminae, Gastrosaccinae, Mysinae, Leptomysinae, and less strongly also Siriellinae (at the level of pseudobranchial lobes); such modifications are also less frequent and, if present, weaker in the Erythropinae. Male adulthood
in many taxa is also marked by fully developed modified pleopods, besides penes and
appendix masculina. Only small modifications, if any, are found on the well-developed
male pleopods of the Boreomysinae. In Palaumysinae, Heteromysinae, and Mysidellinae,
the pleopods are strongly reduced in both sexes, without or with only small, yet particular,
modifications in the male.
Intersexuality
Although much more rarely than in several other crustacean orders, particularly
amphipods, abnormal sexuality situations — referred to as intersexuality — have been
observed also in the Mysida:
Masculinization. – Masculinized females were occasionally found in samples from
brackish and marine coastal waters of the north-east Atlantic and the Baltic: on several
occasions but always with low incidence in populations of the mysid Neomysis integer
and so far in only one specimen of Gastrosaccus spinifer (Kinne, 1955; Holmquist, 1957;
Hough et al., 1992; Mees et al., 1995). The masculinized adult females of Neomysis integer
exhibited a normal marsupium containing embryos or nauplioid larvae, but also elongated
fourth pleopods otherwise typical of adult males. Histological examination by Hough et
al. (1992) indicated fully functional ovaries; in addition, there was no evidence of any
testicular tissue or of parasitism. According to those authors, the observed intersexuality
might reflect a rare genetic abnormality.
Feminization. – As an opposite phenomenon, feminized males were found in field
samples by Yamashita et al. (2001). Among 9282 specimens of the mysid Orientomysis
mitsukurii sampled in Sendai Bay, Japan, there were seven feminized males with empty
marsupium, six of which with a brood pouch smaller than that of normal adult females.
These intersexes had no ovaries but contained testicular tissue with spermatozoa. They
showed elongated fourth pleopods, but no externally visible genital papillae. Intersexuality
had an incidence of 2.5% among adults of the winter generation, but only at a station
polluted with nonylphenol and bisphenol-A, known as xeno-oestrogens in vertebrates.
Apart from xenobiotics, feminizing effects on males may also be induced by ellobiopsid
parasites (see below, ‘Parasites’).
Sex ratio
The details of sex determination are so far unknown in Lophogastrida, Stygiomysida,
and Mysida. For sex verification see above, ‘Reproductive system’. The only experimental
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work has been done by Ortega-Salas et al. (2008), who obtained sex ratios of 2.5-3.0 in
favour of females in a laboratory culture of the mysid Mysidopsis californica under semicontrolled conditions.
In samples from natural populations the sex ratio may be near 1.0, but more often
the females tend to outnumber the males. Mauchline (1980) reviewed the data on
sex ratios in mysids and lophogastrids, and attributed the strong variations observed
in natural populations to differences between sexes regarding age at attainment of
maturity, longevity, habitat, and bathymetric plus regional distribution. Some more recent
publications compiled here support the previous findings on Mysida:
Hanamura (1999) observed strong variations without a clear seasonal trend in the
incidence of females of Archaeomysis articulata from marine sandy beaches in Japan.
In this population the size at maturity varied with seasons in both sexes, and the
overwintering males seemed to mature and to die earlier than the females. Nonetheless,
the sex ratio was near 1.0 when the data were pooled over the main breeding season.
Grabe (1989) found sex ratios near 1.0 at most sampling dates for Rhopalophthalmus
tattersallae from the Arabian Gulf [= Persian Gulf]. San Vicente & Sorbe (2003) obtained
1.0-1.8 in samples of five species of Schistomysis from the south-eastern Bay of Biscay
(north-eastern Atlantic). Gergs et al. (2008) found an extremely large ratio of 34.9 in May
versus only 1.0 in July in a non-indigenous freshwater population of Limnomysis benedeni
in Lake Constance near the confluence of the Rhine River (western-central Europe). In
a non-indigenous population of Hemimysis anomala in River Trent in England, Nunn &
Cowx (2012) obtained 1.5-3.3 in May-June but only 0.5 in June-July, and argued this to be
related to differential mortality.
Mating and oviposition
Mating (fig. 54.36). – The process of mating has so far been observed only in a few
Mysidae (Mysida) species, namely by Nouvel (1937, 1940) in Praunus flexuosus and
Heteromysis armoricana, by Nair (1939) in Mesopodopsis orientalis, by Labat (1954)
in Paramysis nouveli, by Murano (1964b) in Neomysis intermedia, by Clutter (1969)
and Clutter & Theilacker (1971) in Metamysidopsis elongata, and by Wittmann (1982)
in Leptomysis lingvura. These species have a pair of well-developed, tubular penes in
common. Mating occurs during the night, shortly after the moult of the female, but
only if the female has a new egg clutch ready in the ovarian tubes or if this clutch is
already freshly extruded into the brood pouch. There is no precopula comparable to that
in gammarids. There is also no evidence pointing to sperm competition or agonistic
behaviour. The males seem to distinguish the females ready for mating at a certain
distance, probably due to chemotactic substances emitted by the latter (Clutter, 1969;
Wittmann, 1982). In the above-listed species, the approach of the sexes proceeds very fast.
In most species, the male approaches the female from below, and by rotating its own (fig.
54.36B) or the female’s (fig. 54.36E) body usually adopts a head-to-tail, ventral to ventral
position (fig. 54.36B, C, E), in which the sperm is deposited into the marsupium. The
sperm becomes transferred by the well-developed tubular penes, probably without direct
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Fig. 54.36. Mating in Mysidae (Mysida). A, B, initialization (A) and main phase (B) of copulation in Praunus flexuosus (O. F. Müller, 1776); C, copulation in Heteromysis armoricana Nouvel,
1940; D, E, initialization (D) and main phase (E) of copulation in Leptomysis lingvura (G. O. Sars,
1868); F, female of Leptomysis lingvura shortly after copulation with several males, arrows point to
spermatophores fixed on outside of brood pouch; G, spermatophore of Leptomysis lingvura. Abbreviations: dp, distal portion of spermatophore; pe, penis; pp, proximal portion of spermatophore; sz,
spermatozoa. [A, B, after Nouvel, 1937; C, after Nouvel, 1940; D-G, after Wittmann, 1982; A-F,
modified; G, permission granted by Elsevier Verlag, Munich.]
intervention of pleopods. In Praunus flexuosus (fig. 54.36B) and Paramysis nouveli, the
modified fourth pleopods support the male in keeping the proper position during copulation
(Nouvel, 1937; Labat, 1954). This could be a key to understand why modified male
pleopods are present in most species of Mysidae. The mating animals are in contact for
less than one minute; the male leaves the female immediately after sperm transfer, which
takes only a fraction of a second. In general, the female is impregnated only once per egg
clutch and, following this, flees from other approaching males.
However, females of the swarming species Leptomysis lingvura usually mate with
a number of different males. In this case, the sperm is transferred in a comparatively
large spermatophore. This is clearly advantageous for fast mating — one second or
less in this species (Wittmann, 1982). Normally, the sperm is transferred directly into
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the brood pouch. After experimentally induced copulation with several males, however,
some spermatophores were fixed on the outside wall of the brood pouch (fig. 54.36F).
The outside displacement of spermatophores may possibly be due to less suitable mating
responses and/or rejection of additional males by the females after preceding successful
copulation (Wittmann, 1982).
Without mating the brood becomes lost within a few days (Nouvel, 1940; Murano,
1964b; Wittmann, 1982). A new sperm transfer appears necessary for each brood clutch;
as far as known, there is no receptaculum seminis.
The sexual morphological peculiarities of certain mysids in the Antarctic are interpreted
(Wittmann, 1996) as being adaptive for males. They possibly have a chance to reproduce
only once in their lifetime during a very short period. Supporting this concept, the males
of Mysis relicta die shortly after copulation in a subarctic, oligotrophic freshwater lake in
Finland (Hakala, 1978). If copulation proceeds as rapidly as in the above-quoted species
from temperate climates (Nouvel, 1940; Wittmann, 1982), it would be crucial for males
to detect receptive females by using their antennular sense organs and to introduce their
penes into the brood pouch as fast as possible. Here, giant penes (as in Mysifaun erigens
and several species of Mysidetes) may be useful to gain precedence in mating, or may even
favour higher precision in sperm transfer (Wittmann, 1996). In order to transfer genes to the
next generation, fitness for survival may be less important than fitness for reproduction:
in fact, the presence of these giant penes may be inconvenient for normal activities such as
swimming. A partial solution to these conflicting adaption patterns may be erectile penes
(fig. 54.20E), so far known (Wittmann, 1996) from only one mysid species, Mysifaun
erigens. Erection is generally a rare phenomenon in crustaceans, but a common component
of the reproductive behaviour in Stomatopoda (Caldwell, 1991).
Oviposition. – The process of oviposition was observed in the same species as above
for mating. Moult of the female and subsequent deposition of unfertilized eggs may
already start at dawn (Ariani et al., 1982; Wittmann, 1982), but proceeds mainly during
the night. The female isolates herself, becomes immobile, and then shows flexions of
the body. Simultaneously to the right and to the left, the eggs are slowly extruded into
the oviducts, which dilate somewhat. In Neomysis integer and Leptomysis lingvura, each
oviduct extrudes a small transparent egg sac close to the first pair of oostegites (Kinne,
1955; Wittmann, 1981a). The eggs are then discharged into the swelling egg sacs until
each egg sac fills a lateral half of the brood pouch and contains half the brood. The
delicate, deciduous egg sacs are often overlooked in peracarids (Johnson et al., 2001),
suggesting that they may be possibly more common also in mysids. With or without egg
sacs, the eggs are extruded into the brood pouch through the gonopores on the coxae of
the sixth thoracopods. Here, they become fecundated and then immediately covered by a
chorion consisting of substances secreted by the terminal portions of the oviduct. The eggs
become larger upon fertilization and continue to swell during the course of embryonic
development.
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Fecundity
E GG SIZE
Biological limits of egg size. – The Lophogastrida, Stygiomysida, and Mysida share
in common with the Amphipoda the release of young as miniature adults from the brood
pouch. The young do not feed before release, which may be the main reason for a large
lower limit of egg size of about 0.2 mm in Amphipoda and 0.3 mm in Mysida (considering
only fertilized eggs; Steele & Steele, 1975; Wittmann, 1984; Johnson et al., 2001). In
contrast, copepods, barnacles, isopods, cumaceans, and decapods have free-living, feeding
larval stages and, accordingly, produce generally smaller eggs (with a larger range of sizes
in decapods). As a curious consequence of large minimum egg size, the postnauplioid
larvae of three Palaumysis species from tropical marine caves are too large to be entirely
covered by the marsupial plates of their small mothers, whose body length is only 1.32.3 mm (Hanamura & Kase, 2002, 2003). Diameters of fertilized eggs range from 0.31.8 mm in Mysida (Mauchline, 1973b; Wittmann, 1984). Typical values from temperate
climates are 0.4-0.8 mm. Mauchline (1973b) listed 0.8-4.0 mm for seven comparatively
large species of Lophogastrida. This range is unrepresentative for the entire order as long
as data for the small-sized species of Paralophogaster are missing. Only one report on
egg size is available for the Stygiomysida: Ariani & Wittmann (2010) found an average
of 0.68 mm in Spelaeomysis bottazzii. When comparing different species, egg diameters
generally increase with increasing parental body size, increasing latitude, or decreasing
average ambient temperature (Wittmann, 1984). There are smaller differences or even none
upon comparison of egg sizes between different individuals or populations belonging to the
same species.
Seasonal variations of egg size. – In several species from temperate (subtropical to
boreal) climates, the winter eggs are larger than the summer eggs (Mauchline, 1980;
Wittmann, 1981b, 1986a, b; Delgado et al., 1997; Calil & Borzone, 2008). At any given
season, egg sizes normally do not or only weakly increase with body size of the parent
(Wittmann, 1981b, 1986a, b; San Vicente & Sorbe, 1990; Fenton, 1994; Hanamura, 1999;
Hanamura et al., 2009; Biju & Panumpunnayil, 2010; Ramarn et al., 2012; Biju et al.,
2013). A stronger correlation, however, is found in a few populations with large winter
animals producing large winter eggs (Delgado et al., 1997; Calil & Borzone, 2008). In
these latter the reproductive potential of large specimens is clearly diminished in favour of
the fitness of the offspring in order to survive the unfavourable season.
Ecological significance of egg size. – When comparing many different species from
different latitudes, egg sizes increase strongly, namely with slightly less than the square
root of parental body size in epipelagic and coastal species (Wittmann, 1984). Nonetheless,
the deep-water species generally produce fewer but larger eggs per brood clutch compared
with the epipelagic and coastal species. As in other invertebrates, larger eggs result in
larger young. This may be advantageous in the generally trophically poor deep-water
environments. Taking parental size into account, exceptionally large eggs are found
mainly in bathypelagic species, also in certain hypogean species (e.g., the above-quoted
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Spelaeomysis bottazzii) and in a few benthic ones (e.g., the Mysida species Ischiomysis
peterwirtzi; cf. Wittmann, 2013a).
Steele & Steele (1975) listed six ecological implications of egg size in amphipods, four
of which are relevant for Mysida and Lophogastrida according to Wittmann (1984): (1) the
size at release of young depends only on egg size and does not vary with temperature;
(2) the size at attainment of maturity is positively correlated with egg size, and both
increase with increasing latitude (decreasing temperature); (3) the number of eggs per
brood at a given brood weight decreases with increasing egg size. Nonetheless, egg
size and brood size are positively correlated at the interspecific level in mysidaceans:
both, together with brood weight, increase with increasing latitude; (4) egg size is
positively correlated with incubation time at the intraspecific (Wittmann, 1981b) as well
as interspecific (Wittmann, 1984) level. By this strategy, any increase of egg size lowers
the natality (birth rate) at least in iteroparous mysids, but supposedly favours the fitness
of the resulting juveniles.
B ROOD SIZE
Mysida. – Mauchline (1980) and Petryashov (1990) listed the fecundity in many
species of the Mysida. The numbers of eggs produced with each brood clutch vary from
2 to 200, according to individual body size, species, season, and geographical zone.
The constant presence of bilaterally identical pairs of ovaries and gonopores suggests
a minimum number of two eggs per normal oviposition. In fact, only two eggs per
clutch are found in several small-sized tropical taxa, including the above-mentioned
Palaumysis. Female body length and egg numbers are correlated in most species examined
in this respect. A linear relation, often varying seasonally, successfully described the data
obtained within a given population or species (Murano, 1964b; Murtaugh, 1989; Fenton,
1994; Hanamura, 1999; Okumura, 2003; Feyrer, 2010; Biju et al., 2013). Exponential
(log-log) relations have also been applied (San Vicente & Sorbe, 1995, 2003; Delgado
et al., 1997) as recommended by Wittmann (1984) based on a mostly linear relation
between egg numbers and parental weight in combination with an about third power (loglog) relation between parental length and weight. No statistically significant correlations
between parental size and clutch size can be detected if there are only small size differences
between the breeding females, such as observed in Acanthomysis thailandica from a
tropical mangrove estuary in Malaysia (Ramarn et al., 2012). In Neomysis awatschensis
from a Californian estuary and in Neomysis mercedis from Lake Washington, the relation
between brood size and parental size varied strongly between seasons and/or years, related
to differences in temperature (Heubach, 1969) or food availability (Murtaugh, 1989).
Americamysis bahia, reared by Johns et al. (1981) in the laboratory, showed different
survival and fecundity after being fed with different strains of Artemia. Feyrer (2010)
reported that body size is a stronger determinant of brood size than species-specific
differences in four species from coastal marine waters off Vancouver Island (north-eastern
Pacific).
A fundamentally different relation between egg numbers and parental size is obtained
when comparing different species from different latitudes: Some small species from the
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tropics produce only two eggs per clutch; in most species from temperate latitudes the
numbers range 10-20, rarely beyond 50. W. M. Tattersall (1951) counted 190 embryos
in the marsupium of a female of the boreal Mysis stenolepis with 28 mm body size. The
wide size range obtained upon simultaneously plotting many species yields a curvilinear
relation best described by an allometric relation, i.e., by a log-log regression. Such plots
showed that numbers of young as well as the egg weight (volume) increase with slightly
less than the square root of parental body weight (volume) in epipelagic and coastal species
(Mauchline, 1973b; Wittmann, 1984). Accordingly, the portion of body weight (volume)
invested into each brood clutch does not vary with average size of species and with
latitude. This portion averages 10% for body length raised to the third power (as a correlate
of volume; Mauchline, 1973b) and 23% for dry weight (Wittmann, 1984). These values are
compatible with each other considering that eggs have a much lower water content and a
higher lipid content than parental bodies. The order of magnitude of body mass invested
into reproduction holds for all size classes and also for meso- and bathypelagic species.
Lophogastrida. – Female body size and numbers of eggs are also correlated in
lophogastrids, although the results are based on only few species of Gnathophausiidae
(Clarke, 1962; Childress & Price, 1983; Wilson & Boehlert, 1993). As a stupendous
case, Clarke (1962) found 238 embryos in a female Gnathophausia ingens measuring
145 mm length. According to Mauchline (1973b) and Wittmann (1984), however, the
length-fecundity relation is less obvious in meso- to bathypelagic species that constitute
the majority of Gnathophausiidae. In Eucopia unguiculata (Eucopiidae), more eggs are
produced in the Bay of Biscay (17-23) than in the Mediterranean (8-16), despite the same
egg size. In both sea areas, ovigerous females are found throughout the year; there is no
marked seasonal cycle in reproduction (J.-P. Casanova, 1977). Nonetheless, also in the
Lophogastrida, the periods of propagative activity, egg sizes, and size at attainment of
sexual maturity may vary between latitudes, localities, and seasons (Fage, 1941, 1942;
Mauchline, 1973b; J.-P. Casanova, 1977; Wittmann, 1984).
Stygiomysida. – Data on fecundity are very scarce for the Stygiomysida due to their
cryptic, subterranean mode of life (Villalobos, 1951; Pillai & Mariamma, 1964; Nath,
1973; Ortiz et al., 2005; Ariani & Wittmann, 2010). In a brackish well in Apulia, Italy,
female Spelaeomysis bottazzii measuring 9-11 mm body length carry 8-14 eggs with an
average diameter of 0.68 mm (Ariani & Wittmann, 2010). As expected for animals living
in nutrient-poor, subterranean environments, at a given parental size the mean numbers
of young per brood are smaller and egg diameters are larger than in epipelagic and coastal
species of Mysidae and Lophogastridae. The Spelaeomysis values, however, do not exceed
the 95% confidence limits calculated by Wittmann (1984) for these two families. Other
bionomical differences from average epigean Mysidae are much stronger: in Spelaeomysis
bottazzii the incubation period is more than six times as long (>100 days at 20°C) and
a resting stage with reduced marsupial plates is adopted at the moult after release of the
young (Ariani & Wittmann, 2010).
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Incubation
Brood care. – The females show intensive care of their embryos or larvae in the brood
pouch. They produce a respiratory current through the marsupium by pumping movements
of the oostegites. This may be supported by ventilation lobes in a number of Mysida
(Siriella, Paramysis, Mysis, etc.). In addition, coxae and endites of the thoracopods, and
thoracic sternites, may bear brushes of long, plumose and/or microserrated, setae; these
may play some role in ventilating and/or cleaning the brood (e.g., Neomysis integer; cf.
Jancke, 1926; Kinne, 1955). At least a few microserrated setae project into the marsupium
in all species of Mysida so far examined in this respect. In several species of Neomysis,
long, strand-like diverticula with thin walls project from the posterior sternites into the
marsupium. B. Casanova & De Jong (1996) reported a strange tool for optimizing the
storage of larvae — both with respect to the oostegites and larval interspaces — in the
lophogastrid Gnathophausia zoea and the mysid Praunus flexuosus: the integument of
larvae and oostegites is covered by anchoring structures such as acute scales or spines;
such structures are also found on the eyes of the postnauplioid stage in Praunus flexuosus.
Active manipulation of larvae with the thoracic endopods, observed by Wittmann
(1981a) in females of Leptomysis lingvura and by Wortham-Neal & Price (2002) in Americamysis bahia, suggest a more intense interaction of females and young than assumed by
previous authors. From this perspective, the structures projecting into the marsupium possibly also act as receptors providing information about the spatial distribution and state of
the brood. In Leptomysis lingvura, the fully developed postnauplioid larvae ready for release are taken out of the frontal opening of the brood pouch, one by one, during the night,
by the female with the anterior thoracic endopods; they are then turned around with the
endopods and touched with the mouthparts several times (Wittmann, 1981a). Finally, the
female jumps backwards with a sudden tail flip and simultaneously releases the larva. The
slowly sinking, freshly released larva then starts immediately with moulting to become a
free-living juvenile capable of swimming and self-maintenance.
Adoption behaviour. – Some species of Mysida ‘supervise’ their larvae. Laboratory
experiments by Wittmann (1978b) demonstrated that females of three Leptomysis species
grasp freely sinking premature larvae and introduce some of them into their own brood
pouch. This behaviour, termed ‘adoption’ (Wittmann, 1978b), is probably also found
in nature and probably results from a larvae replacement behaviour, which serves to
prevent the loss of own young, for example by saving own larvae fallen out from the
marsupium. Mauchline & Webster (in Mauchline, 1980) found adoptions in seven species
of mysids from British waters, Sato & Murano (1994) in four species from coastal
waters of Japan. Wortham-Neal & Price (2002) observed adoptions in field samples of
Americamysis bahia from the Gulf of Mexico. Johnston & Ritz (2005) showed that
Tenagomysis tasmaniae adopts its own young in preference to those of a conspecific.
In Leptomysis lingvura, adoption also works with young from other parents, to a very
limited extent also with young from other species (Wittmann, 1978b). The females of
Leptomysis lingvura and Leptomysis buergii adopt in specific patterns according to age
and species of young. Embryos and parts of larvae (particularly eyes) are also accepted in
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a similar pattern, indicating that chemosensory mechanisms may be involved. Larvae
that are not of an appropriate age to complete larval development in any particular
marsupium are rarely adopted. Adoption experiments (A. P. Ariani, unpublished) were
also performed in Diamysis, showing the same results. In contrast, one female of the
Stygiomysida Spelaeomysis bottazzii, incubating in the laboratory (Ariani & Wittmann,
2010), resolutely rejected two larvae, one of which was actively motile, coming from a
just deceased conspecific female.
In experiments by Wittmann (1978b), the Mediterranean mysid Leptomysis lingvura
infrequently adopted larvae of its congener Leptomysis buergii and consistently rejected
larvae from other genera. Mauchline & Webster (in Mauchline, 1980) observed that the
north-east Atlantic mysids Praunus flexuosus and Praunus neglectus adopted each other’s
larvae and those of Praunus inermis, although the latter species did not accept larvae from
the other two species. Sato & Murano (1994) observed intraspecific adoptions but no
interspecific adoptions in a total of four species from three genera in Japan. Johnston
& Ritz (2005) obtained the same results for three species from three different genera
in Tasmania. The above results suggest that interspecific adoptions occur only between
certain closely related, congeneric species.
Loss of young. – From field data on eight species of Mysidae (Mysida) from British
coasts, Mauchline (1973b) estimated that about 10% (6-26%) of larvae become lost from
the brood pouch in a premature condition. Laboratory experiments yielded 11% (5-18%)
for Leptomysis lingvura from the Gulf of Naples (western Mediterranean; Wittmann,
1981b) and 12-23% for Mysidopsis californica from the coast of Matzatlán (Mexico;
Ortega-Salas et al., 2008). Such losses were identified as being due to mortality and/or
to premature release of living young: Amaratunga & Corey (1975) observed that female
Mysis stenolepis “were capable of releasing young at any point subsequent to the first
embryonic moult”. Jepsen (1965) sampled prematurely released larvae of Boreomysis
arctica in the plankton. Berrill (1969a) observed cannibalism by laboratory-kept females of
Mysis diluviana on their own young. No cannibalism was observed during release of fully
developed young in Mysis stenolepis, Leptomysis lingvura, Leptomysis truncata sardica, or
Americamysis bahia (cf. Amaratunga & Corey, 1975; Wittmann, 1978b; Wortham-Neal &
Price, 2002). In three Tasmanian species, laboratory-kept mothers did not feed on their own
young before the young moulted after release, but they did feed after this moult (Johnston
& Ritz, 2001). Similarly, Leptomysis lingvura may eat its own brood under conditions
of starvation in the laboratory (Wittmann, 1984). In Americamysis bahia, the survival
rate of larvae increased with increasing age and with decreasing temperature in in vitro
experiments by Wortham-Neal & Price (2002). In natural populations of many species of
Mysidae, a significant part of marsupial mortality appears to be due to parasites (see
below under ‘Parasites’).
Duration of incubation. – In Mysida, the duration of marsupial development varies
mainly with species, season, and temperature: 96 hours in Mesopodopsis orientalis
from Madras (Nair, 1939); 4 days at 24°C in a laboratory population of Antromysis
juberthiei taken from subterranean waters of Cuba (Juberthie-Jupeau, 1976); 5-6 days
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in Acanthomysis sculpta from Vancouver Island, in August (Green, 1970); 6-7 days
in Mysidium columbiae from Jamaica, February to May (Davis, 1966); 12 days in
Praunus flexuosus from Roscoff, August (Nouvel & Nouvel, 1939); 8-13 days in three
Mediterranean species of Diamysis at 20°C in ambient water (Ariani & Wittmann, 2000);
three months in Boreomysis arctica from Norway (Jepsen, 1965); and five months in
Mysis diluviana from Canada (Berrill, 1969a). In a number of Mysidae, a strong decrease
of brood duration with increasing temperature was observed in the laboratory (Murano,
1964a; Wittmann, 1981b; Toda et al., 1984; Johnston et al., 1997; Wortham-Neal & Price,
2002; Fockedey et al., 2006).
Salinity also affects the duration and success of marsupial development as shown by
Vlasblom & Elgershuizen (1977) and Fockedey et al. (2006) for Neomysis integer from
brackish waters at the coasts of the Netherlands and Belgium, by McKenney (1996) for
Americamysis bahia from the Gulf of Mexico, and by Ariani & Wittmann (2000) for
Diamysis mesohalobia from brackish springs and lagoons at the Adriatic and Ionian coasts
of Apulia (eastern Mediterranean). No salinity effects on duration but strong effects on
breeding success were reported by Greenwood et al. (1989) for Mesopodopsis slabberi
from an estuary at Plymouth (north-east Atlantic). At the intraspecific level, the effects of
salinity on duration are generally smaller compared to temperature. No significant trend of
brood duration was found by Wittmann (1984) in literature on different species of Mysidae
breeding at different salinities. According to McLusky & Heard (1971), Praunus flexuosus
can regulate the marsupial fluid hyper- or hypo-osmotically. Nimmo et al. (1978) observed
a delay of brood release under chronic exposure to cadmium in the estuarine mysid
Americamysis bahia. According to Gentile et al. (1983), increasing mercury concentrations
lengthen the brood development of the same species.
A laboratory study by Ariani & Wittmann (1997) on females of the subterranean
Stygiomysida Spelaeomysis bottazzii, kept in August-November in the dark at 20°C in
water taken at the sampling station (with salinity S = 20), indicated that embryonic
development takes more than 16-22 days, and the total period of marsupial development
more than 100-108 days. In contrast to any species of Mysidae so far examined in
this respect, the young of any given female Spelaeomysis bottazzii developed strongly
asynchronously within the same brood pouch.
Breeding cycles. – The propagative activity of the various species of the Mysida and
Lophogastrida may be continuous or may vary between latitudes, localities, and seasons.
Breeding females are found year round in field samples from many populations of Mysidae
in temperate to tropical climates (Goodbody, 1965; Heubach, 1969; Brown & Talbot,
1972; Almeida Prado, 1973; Quintero & Zoppi de Roa, 1973; Juberthie-Jupeau, 1976;
Wittmann, 1984; Ramarn et al., 2012; Biju et al., 2013). Laboratory experiments by Ariani
& Wittmann (2000) on several species of Diamysis from temperate waters in Italy showed
that the breeding females moult after releasing the mature young and generally lay a new
clutch of eggs into the marsupium. Here, the eggs become fertilized upon mating and
develop to free-living F1 young. Continuous breeding cycles characterize at least certain
mysid species in temperate waters. As an alternative, the year-round presence of breeding
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females may result from the temporal overlap of seasonally alternating, asynchronous
generations, as observed by Reynolds & de Graeve (1972) in Mysis diluviana, for example.
This timing of reproduction was termed ‘pseudocontinuous breeding’ by Wittmann
(1984).
Most species from cold-temperate and to a lesser extent also from warm-temperate
regions show a distinct minimum of reproduction or often do not breed at all during
winter (e.g., Tattersall & Tattersall, 1951; Murano, 1964a; Heubach, 1969; Borodich &
Havlena, 1973; Wittmann, 1978a; Mauchline, 1980; Murtaugh, 1989; Fenton, 1992; Mees
et al., 1994). This timing was termed ‘warm-season breeding’ by Wittmann (1984). The
first brood is released during the spring maximum of biological production, and may
in turn reproduce already during summer or during the weaker, qualitatively different
(Odum et al., 2004) autumn maximum of production. Generally, there are only two to
four generations per year (Mauchline, 1980). However, Borza (2014) inferred as many as
4-6 generations per year from field data on non-indigenous freshwater populations of three
highly productive Ponto-Caspian species of Mysidae, which had invaded the Hungarian
reach of the Danube River. The females are iteroparous, normally produce a continuous
series of brood clutches until autumn, and then disappear from field samples. A reduction
of the oostegites at the end of the reproductive period is rare in the family Mysidae (see
above, ‘Oostegites’). Several species show a summer minimum of reproduction between
maxima in spring and autumn (Murano, 1964a; Zatkutskiy, 1970), but there are also
species with a distinct summer maximum (Hopkins, 1965; Richards & Riley, 1967).
A different situation was observed in the Arctic (Lasenby & Langford, 1972) and
assumed also for Antarctic regions (Wittmann, 1996). The animals accumulate storage
materials during summer and gain sexual maturity in early autumn. In autumn or winter
the eggs are deposited in the brood pouch and copulation takes place. Shortly afterwards
the adult males may die. The embryos and larvae continuously develop in the brood pouch;
after about eight months they are released in spring or early summer, when they can profit
from the plankton bloom for fast individual growth. Such animals undergo ‘cold-season
breeding’ as defined by Wittmann (1984). Under strong Arctic conditions the young need
two summers to attain sexual maturity (Larkin, 1948; Geiger, 1969; Fürst, 1972; Lasenby
& Langford, 1972; Mauchline, 1980). This process may last even up to four years under
extreme oligotrophic regimes (Morgan, 1980).
A normal interruption of the breeding activity, not related to seasonal variations,
was described by Ariani & Wittmann (2010) for the Stygiomysidae species Spelaeomysis
bottazzii. Here, the females release their young after a long incubation period passed
in deep and trophically poor groundwater, where they live mainly from fat reserves.
Each breeding cycle, therefore, requires accumulation of reserves in the shallow, more
nutrient-rich groundwater. This may explain why the females adopt a subadult habit at the
moult subsequent to the release of young, probably in order to prevent an unsuccessful
new breeding cycle under poor trophic conditions. These animals could be considered
‘trophically suitable breeders’.
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Adjustment of reproductive parameters
Unlike the Lophogastrida Eucopia unguiculata, the Stygiomysida Spelaeomysis bottazzii, and the Mysida Praunus flexuosus (cf. Nouvel & Nouvel, 1939; J.-P. Casanova,
1977; Ariani & Wittmann, 2010), almost all iteroparous Mysida species so far examined
in this respect do not show a resting stage after the release of young. Rather, they moult
shortly afterwards and deposit a new egg clutch in the marsupium (e.g., Kinne, 1955;
Juberthie-Jupeau, 1976; Pezzack & Corey, 1979; Wittmann, 1981b; Ariani & Wittmann,
2000; Johnson et al., 2001; Wortham-Neal & Price, 2002). Nonetheless, females with
empty brood pouches are often found in the field; this may be correlated with high population densities (Clutter, 1969). The first brood is aborted by Siriella armata in the laboratory, also resulting in females with empty brood pouches (Cuzin-Roudy et al., 1981). The
normally non-interrupted sequence of broods indicates an effective coupling between female moult cycle, yolk accumulation in the ovaries, and development of the young (CuzinRoudy & Tchernigovtzeff, 1985; Okumura, 2003). The eggs of the first brood are produced
during 2-3 instars in Leptomysis lingvura (cf. Wittmann, 1981b). These combined instars
last a total of 1-2 incubation periods (Clutter & Theilacker, 1971; Wittmann, 1978a; Gaudy
& Guerin, 1979), suggesting that coupling also plays some role in the first brood clutch of
a given female. In aquatic poikilotherms, the duration of development of embryos and of
non-feeding larvae is generally highly temperature-dependent. The reproductive biology of
mysids, however, is not completely correlated to the temperature regime: for example, the
temperature acceleration of marsupial development is usually smaller at the intraspecific compared to the interspecific level (but not smaller in Americamysis bahia; WorthamNeal & Price, 2002). Wittmann (1984) showed that the latitudinal temperature effects
are buffered by coordinated adaptive adjustments of parental weight, brood weight, egg
weight, numbers of young, incubation period, and moult instars. These homeostatic adaptations, i.e., outcomes of evolutionary trends, make the following reproductive parameters
less variable at the interspecific level between latitudes, at least for non-interrupted sequences of broods in iteroparous mysids: (1) the average numbers of young per female
incubatory day; (2) the portion of body weight invested into each brood clutch; (3) the
average amount of yolk invested per egg per day. Note also that the three parameters are
mutually dependent.
DEVELOPMENT AND MOULTING
Marsupial development
N UMBERS AND DISTINCTION OF MARSUPIAL STAGES
Based on the external appearance of “embryos” in the brood pouch, Kinne (1955)
distinguished six developmental stages termed by him ‘a’ to ‘f ’ in the mysid Neomysis
integer. Mauchline (1973b) condensed Kinne’s terminology to ‘eggs’ (a), ‘eyeless larvae’
(b-e), and ‘eyed larvae’ (f ), whereby the definition of eyeless larvae is inconsistent with
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hatching from the egg membrane between Kinne’s stages b and c. Based on the events of
egg hatching and two larval moults, Jepsen (1965) distinguished first, second, and third
“embryonic” stages in Boreomysis arctica. Based on the same events, the biologically and
morphologically consistent terminology of Wittmann (1981a) is used here (fig. 54.37),
who distinguished an embryonic stage (fig. 54.37A-D) between fertilization and hatching
from the egg membrane, nauplioid larvae (fig. 54.37E-G; named after 2-3 pairs of free
naupliar appendages) up to the first moult, and postnauplioid larvae (fig. 54.37H) up
to the second moult, which leads to the free-living juvenile stage. This terminology was
adopted by Cuzin-Roudy & Tchernigovtzeff (1985), Johnston et al. (1997), Johnston &
Ritz (2001, 2005), Wortham-Neal & Price (2002) and others. Within stages, Wittmann
(1981a) distinguished arbitrary phases to indicate important morphological changes that
are externally visible and can be recognized easily in formalin- or ethanol-fixed material.
Such subdivisions could be practical for physiological and ecological research and
aquaculture purposes.
The same number and morphology of main marsupial stages (figs. 54.37, 54.38), i.e.,
embryonic stage, nauplioid, and postnauplioid larvae, as in the Mysida, are also found
in the Stygiomysida (Ariani & Wittmann, 2010) and Lophogastrida (Illig, 1930; Fage,
1941; Mauchline, 1980). It is noteworthy that a pale cornea (fig. 54.38J) is present
in the postnauplioid larvae of the anophthalmic, subterranean Stygiomysida species
Spelaeomysis bottazzii, whereas the cornea is missing in free-living juveniles (fig. 54.38K)
and adults (fig. 54.1C) (Ariani & Wittmann, 2010). Eye reduction is even stronger in the
subterranean Spelaeomysis longipes, where the postnauplioids show separate eyestalks
without ommatidia and visual pigment. The eyestalks merge successively during the
subsequent free-living juvenile stages. In the adult, the eyestalks are fused to a single,
transversal eye plate, which has rearranged optic ganglia inside (Nath et al., 1972a).
M ORPHOLOGY OF MARSUPIAL STAGES
Embryonic stage (fig. 54.37A-D). – Embryonic development was studied mainly in
species of the family Mysidae (Mysida), namely by Van Beneden (1861), Nusbaum (1887),
and Bergh (1893) in Praunus flexuosus, by Nair (1939) in Mesopodopsis orientalis, by
Needham (1937) and Jepsen (1965) in Boreomysis arctica, by Scholtz (1984) and Scholtz
& Dohle (1996) in Neomysis integer, by Manton (1928b) in Hemimysis lamornae, and by
Wittmann (1981a) in Leptomysis lingvura. Data on the embryonic and larval development
of mysids are also available in the review given by Johnson et al. (2001) for the marsupial
development of the Peracarida.
Nair (1939) observed the maturation of the oocytes, the fecundation, and the first
processes of segmentation in the mysid Mesopodopsis orientalis. The detachment of the
first polar bodies occurs when the eggs are deposited into the brood pouch. The second
polar body is formed after the penetration of the spermatozoa (with polyspermy). The
amphimixis occurs in the centre of the egg, as typically in centrolecithal eggs. Here, the
first nucleic divisions take place and the blastomeres differentiate and form a vesicle.
The latter then spread to a superficial portion of the ectoderm to constitute a blastoderm
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Fig. 54.37. Main stages in the marsupium (A-H) and freshly hatched juveniles (J, K) of the mysid
Leptomysis lingvura (G. O. Sars, 1868). A-D, phases E1, E3, and E5 of embryonic stage; E-G,
phases N1, N2, and N4 of nauplioid larval stage; H, phase P2 of postnauplioid larval stage; J,
hatchling fixed immediately after release from brood pouch and subsequent second larval ecdysis,
note absence of statoliths; K, juvenile fixed 10 h after hatching and subsequent ecdysis, note pair of
well-formed, large statoliths. Abbreviation: a1, antennula; a2 antenna; ar, abdominal rudiment; ca,
carapace; chr, chromatophores; ha, heart; he, hepatopancreas; md, mandible; ncu, naupliar cuticle;
opr, optic rudiment; plp, pleopods; seg, segmentation (metameres); stl, statoliths; sto, stomach;
thp, thoracopods; tl, telson; up, uropods. [After Wittmann, 1981a; A-H, modified; J, K, permission
granted by Elsevier B.V., Amsterdam.]
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disc. The segmentation is described as typically discoidal in Praunus. A transversal row
of ectodermal teloblasts then differentiates, behind of which the endodermal cells meet in
enclaves of the vitellus, which they absorb. Certain cells, mesodermal teloblasts, migrate
downwards from the blastoporic area in order to form a mesoderm, while a genital
rudiment is formed at the surface and subsequently sinks down below the disc. The
anterior lip of the blastoporic area will provide the trunk. Initially, the anterior portion
of the embryo consists of two halves (the optic rudiments), which are then united in
the sagittal plane. The endodermal cells penetrate downwards, incorporate the vitellus
and form the middle intestine, which ultimately becomes sutured with the proctodaeum
and the stomodaeum. The hepatic tubes appear to be of mesodermal origin (Nair, 1939).
At this time, the naupliar appendages, i.e., the antennules, antennae, and mandibles,
differentiate. Behind a caudal furrow that transverses the blastoporic area, an anteriorly
turned, conical eminence, the caudal papilla, is formed. Dohle et al. (2004) doubt for
lophogastrids and mysids that this is a “true” caudal papilla. For gene expression and
related segmental differentiation in the germ band, see the detailed review by these
authors (Dohle et al., 2004).
Wittmann (1981a) distinguished six phases in the embryonic stage: cleavages and
formation of the blastoderm during phase E1, formation of the germinal disc (E2) and of
the optic rudiments (E3), separation of the abdominal rudiment (E4), formation of naupliar
appendages (E5), and differentiation and rotation of the abdominal rudiment until hatching
(E6). The embryonic phases E1, E3, and E5 are illustrated in fig. 54.37A-D.
Nauplioid larva (figs. 54.37E-G, 54.38F-H). – Also larval development was studied
mainly in species of the family Mysidae (Mysida), in particular by Nair (1939) in
Mesopodopsis orientalis, by Murano (1964b) in Neomysis intermedia, by Jepsen (1965)
in Boreomysis arctica, by Wittmann (1981a) in several species of mysids, especially in
Leptomysis lingvura, by Cuzin-Roudy et al. (1981) and Cuzin-Roudy & Tchernigovtzeff
(1985) in Siriella armata, by Wortham-Neal & Price (2002) in Americamysis bahia, and
by Fockedey et al. (2006) in Neomysis integer; for certain aspects also in species of the
Stygiomysida genus Spelaeomysis (Nath et al., 1972a; Ariani & Wittmann, 1997, 2010).
A pair of transient glandular, lateral dorsal organs, independent from the germ band,
appear to be related to the hatching from the egg membrane, which releases the nauplioid
larva. Below the now uncovered integument, the larva completes its differentiation. The
cuticle does not follow the subsequent events of body segmentation and formation of
appendages. All somites and their appendages are organized. A pre-antennary somite
and a seventh pleomere appear, the latter subsequently becoming fused with the sixth
pleomere (Manton, 1928b; Nair, 1939). Wittmann (1981a) distinguished four phases of
the nauplioid stage: N1 is characterized by ramification of the antennula and externally
visible signs of body segmentation; N2 by a well-segmented thorax and pleon; N3 by wellformed thoracopods and uropods, and (if any) also by the development of eye pigment; N4
by well-formed maxillae, heart, and pleopods, and by the first heart beats. The nauplioid
phases N1, N2, and N4 are illustrated in fig. 54.37E-G.
A comparative study of the nauplioid stage (Wittmann, 1981a) in representatives of
the Mysidae genera Leptomysis, Hemimysis, Paramysis, and Siriella, showed peculiar
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Fig. 54.38. Morphology of larvae and juveniles of the Mysida (A-E), Lophogastrida (F, G), and
Stygiomysida (H-K). A, early nauplioid larva of Leptomysis lingvura (G. O. Sars, 1868), lateral;
B-E, armature of nauplioid abdomen in Leptomysis lingvura (B as detail of A), Siriella gracilipes
H. Nouvel, 1942 (C), Hemimysis speluncola Ledoyer, 1963 (D), and Paramysis helleri (G. O. Sars,
1877) (E), lateral; F, early nauplioid Gnathophausia zoea Willemoës-Suhm, 1873, ventral; G, late
nauplioid Eucopia sculpticauda Faxon, 1893, lateral; H-K, three successive stages separated by
ecdysis in Spelaeomysis bottazzii Caroli, 1924: early-mid nauplioid larva (H, lateral), postnauplioid
larva (J, obliquely lateral, anterior thoracic exopods omitted), and freshly released juvenile (K, dorsolateral). Abbreviations: a1, antennula; a2, antenna; ar, abdominal rudiment; cer, cercopod; fs, furcal
spines; ym, yolk mass. [A-E, after Wittmann, 1981b; F, after Fage, 1941; G, after Illig, 1930; H-K,
after Ariani & Wittmann, 2010; A-K, modified.]
characteristics of the armature at the tip of the nauplioid abdomen (abdominal rudiment),
such as the presence of spines, setae, or cercopods. Most species bear setae (fig. 54.38B)
or spines (fig. 54.38C, E). A kind of abdominal tip similar to that of Paramysis helleri
(fig. 54.38E) was observed by Ariani & Wittmann (2000) in Diamysis mesohalobia.
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Among extant Mysida, cercopods (fig. 54.38D) were so far found in the nauplioid larvae
of only five genera, all belonging to the subfamily Mysinae (Manton, 1928b; Green,
1970; Modlin, 1979; Wittmann, 1981a). They possibly represent plesiomorphic characters
within the Eumalacostraca, related to the well-formed caudal furca (i.e., processes on
the telson), which is found throughout (Schram, 1986) in fossil Pygocephalomorpha from
the Carboniferous to Permian. The nauplioid abdomen of the lophogastrid Gnathophausia
zoea bears two pairs of furcal spines (fig. 54.38F) at the apex (Fage, 1941), which
suggest a possible homology to cercopods. Such a homology appears less likely for
the nauplioids of Boreomysis arctica (Boreomysinae, Mysida), which have a pair of
“polyspinal appendices” (Jepsen, 1965) in a clearly more anterior position on the
abdominal rudiment.
The tropical, cavernicolous mysid Palaumysis philippinensis (and probably also its
congeners) are exceptional in that the nauplioids have very long first and second antennae.
Also unusual is the large relative size of eggs and larvae, with the postnauplioids
overreaching as much as half the length of the throughout very small adults (<2 mm;
Hanamura & Kase, 2002).
Postnauplioid larva (figs. 54.37H, 54.38J). – Upon the first larval ecdysis the postnauplioid larva emerges inside the marsupium. This stage is dorsally bent and shows all adult
appendages, although these are still incompletely differentiated. Wittmann (1981a) distinguished three phases of the postnauplioid stage: The eyes rotate from outer-ventral into
anterior position and the carapace is freed during phase P1; the stomach becomes well
formed and body pigment (if any) becomes increasingly visible during P2 (fig. 54.37H);
the lobes of the hepatopancreas are distinguished (freed) during yolk consumption, and
the larvae start to respond to external stimuli during P3. The heart beats are now continuous. Small movements of the gut and appendages, and fluttering of the pleon become
visible, interrupted by quiet periods. Nonetheless, artificially released postnauplioids are
not capable of swimming unless they moult to the free-living juvenile stage.
H ATCHING AND LARVAL MOULTS
The embryo hatches by stretching the abdominal rudiment, which causes the caudal
papilla to point backwards from this time onwards. The stretching stresses and finally
ruptures the egg membrane, liberating the nauplioid stage. Later, the first larval ecdysis
from the nauplioid to the postnauplioid stage is performed, accompanied by body flexing.
The old cuticle ruptures above the dorsal yolk mass and it takes considerable time to tear
apart its remains. The egg membrane and cuticle of the nauplioid are always shed within
the brood pouch, whereas the cuticle of the postnauplioid larva may be shed either within
(Davis, 1966), or outside (Wittmann, 1981a; Cuzin-Roudy & Saleuddin, 1985; Johnston
& Ritz, 2001) the marsupium, depending on the species. The second larval ecdysis is
also accompanied by body flexing. The animal emerges dorsally, and the old cuticle falls
off in one piece (Wittmann, 1981a). It is always the second larval ecdysis that leads to
the juvenile stage capable of swimming. The larvae may moult shortly before (Davis,
1966), but normally shortly after release from the brood pouch. In this latter case the
freshly released larvae moult while slowly sinking in the water column. In Leptomysis
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lingvura, the freshly moulted juveniles need an additional 20-40 min at 16°C to complete
their statocysts by precipitation of fluorite during statolith formation (Wittmann, 1981a;
cf. above, ‘Static organs’). Photos of freshly hatched juveniles before and after statolith
formation are presented in figs. 54.37J and 54.37K, respectively. The resulting stage is
free-living, self-sustaining, and closely resembles the adult, but lacks secondary sexual
characteristics.
T IMING OF MARSUPIAL STAGES
Synchronization of marsupial development. – For more than a century we know
that the marsupial young of a given female are usually all at about the same stage
of development in Mysida and Lophogastrida (for exceptions see above, ‘Adoption
behaviour’). Johnston et al. (1997) and Johnston & Ritz (2001) observed synchronous
development and release of broods in three species of Mysidae forming monospecific
swarms in coastal waters of Tasmania. Johnston & Ritz (2001) found that development
time did not vary between in vivo and in vitro incubation and concluded that the parent
does not influence the synchrony of development. Those authors, however, did not discuss
the findings of Cuzin-Roudy & Saleuddin (1985), who observed that the final (= second)
larval moult in laboratory-kept Siriella armata is inhibited when the mother is unable
to finish incubation, even when the larvae are artificially released from the brood pouch.
According to Cuzin-Roudy & Tchernigovtzeff (1985), unlike the normal release during
the night, the artificial release of young during daytime was never followed by the second
larval moult in Siriella armata. Wittmann (1978b, 1981b) observed in the laboratory that
female Leptomysis lingvura delayed moulting by 2-5 days (17-42% of moult instars under
same culture conditions) following artificial implantation of premature larvae into the
marsupium. Summarizing the so far published data suggests species-specific differences
in the ability to contribute to the synchronization of development by means of limited
moult inhibition, when one of the counterparts — parent or young — is not ready to finish
incubation. The young may contribute by communicating tactile, chemical, or some other
kind of signals to the parent. This has never been examined in detail. A hint to chemical
or tactile communication could be the adoption of detached eyes or less frequently of
other parts of larvae by females of Leptomysis lingvura in the laboratory (Wittmann,
1978b). The brood pouch is well equipped with setae and the females certainly perceive
the small movements (Davis, 1966; Berrill, 1969a) of the late postnauplioid larvae. These
movements merit future examination as potential signals of the approaching completion
of larval development.
Fenton (1994) and Johnston & Ritz (2001) examined three swarming mysid species
and reported that one, namely Paramesopodopsis rufa, showed some differentiation
according to the marsupial stages among females within swarms. This resulted in partially
synchronous release, which may assist the initially helpless larvae to escape from
cannibalism by older conspecifics in the swarm and from being taken by predators. For
many species, a certain degree of ‘synchronization’ could be expected due to the separation
of size- and age-stages in different swarms or in subgroups within swarms. This separation
is related to combinations of social interaction and environmental stimuli (Clutter, 1969;
Mauchline, 1971; Zelickman, 1974; Wittmann, 1977, 1978a; O’Brien, 1988).
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Relative duration of marsupial stages. – A close coupling between moult cycle and
ovarian cycle of the parent, and the development of marsupial young, was reported
by Cuzin-Roudy & Tchernigovtzeff (1985) in laboratory-cultured Siriella armata, and
by Okumura (2003) in breeding females of Acanthomysis robusta collected in the field
at sea coasts of Japan. Nonetheless, the relative durations of the marsupial stages in the
laboratory show surprisingly strong differences between the various species of Mysidae,
and minor, yet significant, temperature-related differences (Wittmann, 1981a; CuzinRoudy & Tchernigovtzeff, 1985; Johnston et al., 1997; Wortham-Neal & Price, 2002;
Fockedey et al., 2006). The embryonic stage occupies mostly an intermediate portion (1643%) of the incubation period, the nauplioid stage is mostly the longest (22-71%), and the
postnauplioid stage is mostly the shortest (8-36%). Depending on the species, the relative
duration of any stage may be shortened or lengthened by a given temperature increase.
Comparable results are obtained for the frequencies of the three marsupial stages in field
samples: Wittmann (1981b) found means of 29-41, 36-51, and 13-32%, respectively,
for eight species from the Adriatic and Tyrrhenian seas (Mediterranean). Very similar
results are also obtained for eight species from British coasts (north-eastern Atlantic)
by recalculating the data of Mauchline (1973b), who used a different schedule for the
distinction of stages.
Moulting and growth
Moulting process. – The process of moulting (fig. 54.39) shows the same pattern in
all examined subfamilies of the Mysidae (Mysida; Nouvel, 1958). The cuticle ruptures
along a marginal line close to the lateral and frontal margins of the carapace, passing
generally below the frontal plate at a certain distance from the tip. A rupture line proceeds
also longitudinally and ventrally along each eyestalk. The lateral walls of the thorax show
Fig. 54.39. Rupture lines of cuticle upon moulting in Mysida. Abbreviations: lma, marginal line; loc,
ocular line; lsc, line of stretched cuticle. [Modified after Nouvel et al., 1999.]
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two longitudinal lines where the cuticle becomes considerably stretched, forming a pair of
lateral bellows that can more or less lift off from the sclerites, with the borders of the latter
resembling a rupture line.
In antennal aesthetascs of the mysid Neomysis integer, the morphological basis for
the sensory function remains intact until ecdysis because the dendritic connections with
the shaft of the old setae are maintained (Guse, 1980). Such connections are maintained
in most arthropod sensilla so far examined, but become lost upon moulting in the antennal
aesthetascs of the isopod Idotea balthica and in various other sensilla of some spiders and
insects (Guse, 1983a).
When moulting approaches, the animals cease feeding, lose transparency, and bend and
stretch several times while sinking down to the bottom. Suddenly they liberate themselves
from the exuvia through the opening formed by the marginal line of the carapace; here, the
outer face of the carapace lifts like a flap and turns backwards around its posterior border,
which acts like a hinge. Within a few minutes the animal regains swimming capability.
The morphology of females after the moult at the end of incubation is generally similar
to that immediately before moulting. Nonetheless, a reduction of oostegites after the
reproductive period was reported by Nouvel & Nouvel (1939) for the Mysida species
Praunus flexuosus. A moulting process leading back to a habit with strongly reduced brood
lamellae was observed by Ariani & Wittmann (2010) in the subterranean Stygiomysida
Spelaeomysis bottazzii. This is probably related to a breeding strategy to avoid continuous
breeding cycles under critical food conditions (see above, ‘Breeding cycles’).
Moulting cycle. – For the hormonal control of moulting see above, under ‘Endocrine
organs’. The duration of the moulting cycle generally increases with body size and decreases with increasing temperature. In breeding females, the moult instars are prolonged
until the young are released from the brood pouch. The correlations between moulting and
the lunar cycle or the tidal amplitude are poorly explained (Depdolla, 1916; Nair, 1939;
Nouvel & Nouvel, 1939; Nouvel, 1940, 1945). According to laboratory observations by
Ariani et al. (1982), moulting at the end of incubation in female Diamysis mesohalobia
generally occurs at dawn.
Experiments by Cuzin-Roudy & Tchernigovtzeff (1985) revealed a moult cycle of 12
days at 20°C in reproductive females of the mysid Siriella armata. At the end of each
cycle, the release of young, moulting, copulation, and egg deposition took place within
eight hours. The cycle of the integument appears to be synchronized with the ovarian
cycle and with marsupial development. Cuzin-Roudy & Tchernigovtzeff (1985) found that
the embryonic phase corresponds to the postmoult period (postecdysis) of the parent, the
nauplioid phase to the “intermoult period” (diecdysis), and the postnauplioid phase to
the premoult period (proecdysis). A similar timing was observed by Okumura (2003) for
Acanthomysis robusta. Near the end of the embryonic phase, a row of oocytes becomes
visible in each ovary at female moult stages A-B. Yolk accumulation starts at moult stage
C during the early nauplioid phase, and continues up to moult stage D2 during the late
nauplioid phase.
In juvenile and subadult Mysis mixta and Neomysis integer taken from the Baltic Sea
for laboratory experiments (Gorokhova, 2002), both a decrease of temperature and reduced
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food availability prolonged the complete moult cycle and the different stages within this
cycle. Reduction of food prolonged the relative duration of diecdysis and early proecdysis
stages, at the expense of the stages close to ecdysis. The temperature showed no clear
effect on relative stage chronology as long as food supply was high. As expected, the
chronology of moulting is particularly important for epibionts (Hanamura et al., 2010):
The infestation prevalence and loads of the tropical, estuarine mysid Mesopodopsis
tenuipes by the vorticellid Zoothamnium duplicatum are lower in females carrying earlier
embryos or larvae in the marsupium, ergo having a fresher cuticle than those with older
young.
In the stygiomysid Spelaeomysis longipes from a freshwater well in India, calcium is
stored in a pair of rod-like calcareous bodies in midgut caeca extending forwards from
the junction of midgut and hindgut. These bodies appear during the premoult period and
attain their maximum length shortly before ecdysis (Nath, 1972).
Growth between moults. – Size increments of the early, free-living juveniles between
successive moults are typically in the order of 10-30% in Mysida and Lophogastrida
(Murano, 1964a; Clutter & Theilacker, 1971; Amaratunga & Corey, 1975; Childress &
Price, 1978). With increasing body size, the growth factors of most species decay in a
logarithmic manner (Mauchline, 1980), or there may be an initial increase up to a modal
value followed by a distinct decay (Matsudaira et al., 1952; Gaudy & Guerin, 1979).
Growth slows at low temperatures, but size at attainment of maturity as well as longevity
generally increase with decreasing temperature, so that adult sizes and egg sizes generally
increase with increasing latitudes. The sizes are often greater in winter than in spring or
summer in regions with a distinctly seasonal climate (Mauchline, 1980; Wittmann, 1984;
Mees et al., 1994).
‘Inter-moult’ growth. – Mauchline (1973a) measured 13 species of Mysidae from the
north-eastern Atlantic and reported that females with postnauplioids (quoted as “eyed”
larvae) have a longer pleon at given carapace length compared to females carrying eggs.
He attributed this difference to ‘inter-moult’ growth by stretching of the inter-segmental
joints [note, that Mauchline’s “inter-moult” period lasts longer than the diecdysis]. Using
regression analysis, he estimated an average increase of body length by about 7%. Fenton
(1994) found 2-6% in field populations of three species in Tasmania. Wittmann (1978a)
estimated from laboratory-reared specimens of Leptomysis lingvura and Leptomysis
buergii that the ‘inter-moult’ swelling amounts to about half the total length increase
between successive moults, without significant differences according to sex and body size.
Regeneration
As in several groups of animals, particularly invertebrates, crustaceans show some
capacity to re-form parts of their body that have been lost or damaged by injury,
autotomy, or otherwise (see review by Charmantier-Daures & Vernet, 2004, in the
first volume of the present series). Regeneration following autotomy at a preformed
fracture plane is common in certain Decapoda, and less frequent in certain Isopoda and
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Fig. 54.40. Eye heteromorphosis in the mysid Diamysis mesohalobia Ariani & Wittmann, 2000.
Basal part of an antenna-like flagellum (arrow) regenerated after excision of left eye in a laboratorykept female. [A. P. Ariani, unpublished.]
Amphipoda. So far there are no reports of autotomy for Lophogastrida, Stygiomysida, or
Mysida.
Băcescu (1940) described the comparatively frequent anomaly “rotundicauda” of the
telson of Limnomysis benedeni in brackish to freshwater coastal lakes of the western
Black Sea. Regeneration was identified as one of several potential reasons for this.
Based on laboratory experiments with Neomysis integer, Mees et al. (1995) concluded
that irregularly shaped or nearly symmetrically rounded, abnormal telsons are due to
regeneration. In this species, abnormal telsons, along with intersexuality (see above,
‘Intersexuality’), are comparatively frequent and widespread in estuaries from northern
to south-western Europe. By comparison, both phenomena seem to be rare or absent,
respectively, in the partly co-occurring mysids Schistomysis kervillei and Gastrosaccus
spinifer.
In a classical finding, Herbst (1896) obtained regeneration of an antenna after extirpating an eyestalk together with the optical ganglion in a marine decapod. An analogous
experiment was conducted on the mysid Diamysis mesohalobia from a brackish spring in
southern Italy. Also in this case there was evidence of heteromorphic regeneration, which
gave rise to the basal part of an antennal flagellum, partly segmented and equipped with
small setae (fig. 54.40; A. P. Ariani, unpublished). Replacement of eyes or appendages
by appendages of another somite is known in various crustaceans (Charmantier-Daures
& Vernet, 2004), particularly decapods (Nevin & Malecha, 1991). Morphogenetic signals
for the replacement of antennal structures by pediform structures are well known in insects (Angelini & Kaufmann, 2005); data on eyestalks versus legs are still lacking. From a
phylogenetic point of view, the heteromorphic replacement of eyestalks seems to support
the as yet unsettled hypothesis (cited in Gruner & Scholtz, 2004) that the malacostracan
eyestalks originate from an antenna-like appendage. This, in turn, is connected with the
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also unresolved question (Dohle et al., 2004; Gruner & Scholtz, 2004) of a putative preantennary somite, often also quoted as “ocular somite”.
Life cycle
Attainment of sexual maturity. – The ‘giant’ deep-sea lophogastrid Gnathophausia
ingens needs 10-11 post-larval instars to attain maturity (Childress & Price, 1978). In
general, the Mysida need 10-13 (range 8-21) instars between hatching of the free-living
juvenile and attainment of sexual maturity (Ishikawa & Oshima, 1951; Matsudaira et al.,
1952; Gaudy & Guerin, 1979; Berill & Lasenby, 1983; Toda et al., 1984). When comparing
different epipelagic and coastal species, the size at attainment of sexual maturity is
positively correlated with egg size and shows additional variations between latitudes,
localities, and seasons (Blegvad, 1922; Nouvel & Nouvel, 1939; Labat, 1957; Mauchline,
1973b; Wittmann, 1984). Low temperatures and starvation may slow down or suppress the
advancement towards sexual maturity (Matsudaira et al., 1952; Gaudy & Guerin, 1979;
Morgan, 1980; Toda et al., 1984). In the estuarine mysid Americamysis bahia from the Gulf
of Mexico (McKenney, 1996), time to maturation and to release of first brood decrease,
and percentage of reproductively active females increases with increasing temperature
(range 19-31°C) and salinity (S = 3-31), whereby both environmental factors interact.
Life span. – In temperate climates, the life span of coastal mysids generally varies
in the range of 2-18 months, rarely up to two years (San Vicente & Sorbe, 1993,
1995). Neomysis intermedia from warm-temperate (6-30°C) freshwater lakes of Japan
shows life spans of only 1.5, 2, 2, or 5 months in summer, spring, autumn, or winter,
respectively (Murano, 1964a, 1999b). It is 5, 7, or 9 months, respectively, for three
overlapping generations observed per year in the mysid Schistomysis spiritus from waters
off Arcachon (north-eastern Atlantic; San Vicente & Sorbe, 1995, 2003). When there
is more than one generation per year in waters with strong seasonality, the summer
generations may live only 2-3 months (Matsudaira, 1952), while the overwintering
generation (released in late summer to autumn) may live 2-3 times longer. In Subarctic
to Arctic waters the normal life span is 1-4 years, depending on trophic conditions and
average size of the species (Geiger, 1969; Hakala, 1978). Life spans of that order are
also found in populations artificially introduced in subalpine lakes (Morgan, 1980, 1981).
Ward (1984) estimated generation times of 2 or 4 years for two Subantarctic populations
of Antarctomysis maxima, respectively. For Antarctic populations, Siegel & MühlenhardtSiegel (1988) gave minimum estimates of 3-4 years for the life span of the intermediatesized Mysidetes posthon, versus 5-6 years for the much larger Antarctomysis ohlinii and
Antarctomysis maxima.
Calil & Borzone (2008) suggest a direct relation between egg volume and generation
longevity in the mysid Metamysidopsis neritica from sandy beaches in southern Brazil.
This continuously breeding species shows three main generations, namely summer, fall,
and winter generations, with the largest eggs produced in winter. In agreement with this,
the overwintering generation of Mesopodopsis slabberi in a coastal lagoon of the Ebro
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delta (north-western Mediterranean) shows a longer life expectancy and produces larger
eggs compared to the generation from spring and summer (Delgado et al., 1997).
Mauchline (1972) compiled literature data on euphausiids and mysidaceans living in
different bathymetric zones and concluded that bathypelagic species probably live 3-7
times as long as epipelagic species. Chikugo et al. (2013) estimated life spans of three years
for pelagic populations of the lophogastrid Eucopia australis and the mysid Boreomysis
californica sampled in 1000 m depth in oceanic waters off northern Japan. Wilson
& Boehlert (1993) estimated a two-year life span for the lophogastrid Gnathophausia
longispina off north-east Hawaii, but they conceded that this duration could increase with
increasing latitudes and also that older specimens possibly live at depths beyond that
reached by their sampling gears. According to Childress & Price (1978), a life span of
eight years is plausible for the ‘giant’ lophogastrid Gnathophausia ingens.
Laboratory investigations by Ariani (1982) showed that specimens of the subterranean
Stygiomysida species Spelaeomysis bottazzii may survive for over 16 months at 20°C in
water from the sampling well. There, the only food source is a thin film of green algae,
diatoms, and Cyanobacteria partially covering soft calcareous (Quaternary calcarenites)
rocks (from the walls and the bottom of the well).
ECOLOGY AND ETHOLOGY
Habitat and distribution
P ELAGIC ENVIRONMENTS
Lophogastrida. – The lophogastrids are exclusively marine and mostly pelagic. During
daytime, the adults of most species in the genera Lophogaster and Paralophogaster stay
on the bottom or close to the bottom, generally in 200-700 m depth, while the juveniles
show a planktonic mode of life. J.-P. Casanova (1993) reported this kind of stratified
distribution for six species from New Caledonian waters. The remaining species of the
same genera plus one Ceratolepis are pelagic and inhabit more superficial layers (about
200 m): Lophogaster spinosus, Lophogaster schmidti, Ceratolepis hamata, and four small
species of Paralophogaster, living in the Red Sea and/or the northern Indian Ocean. All
remaining Lophogastrida are bathypelagic: the genera Chalaraspidum, Gnathophausia,
and Eucopia are found mostly below 2000 m depth and are restricted to narrow ranges
of hydrological conditions, particularly regarding temperature and oxygen content (Fage,
1942). The supposed rarity of certain species may be due to sparse exploration of their
habitat. In addition, Childress et al. (1989) observed a Gnathophausia, later described
as Gnathophausia childressi, as being strictly tied to the turbid layer above the bottom:
this layer was characterized by the constant presence of suspended matter. This species
is closely related to Gnathophausia affinis, which also occupies the same type of benthopelagic habitat.
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Mysida. – Some holopelagic species, such as certain Siriella, only rarely approach
the coast. This genus contains most of the (few) epipelagic species with transoceanic, in
part world-wide distribution. The greatest numbers of mesopelagic species of Mysidae
are in the subfamilies Erythropinae and Boreomysinae. Fosså & Brattegard (1990) found
the distribution of 18 mysid species in Norwegian fjords clearly separated in four distinct
depth zones within the range of 32-1260 m.
Certain mysids are bathypelagic (e.g., Cartes & Sorbe, 1995; Hargraeves & Murano,
1996; Hargraeves, 1999; Frutos & Sorbe, 2013). Those inhabiting the continental slope
may be divided into three main faunistic groups occurring in different depth zones. The
zones of faunistic change vary between latitudes and are positioned around 500 and
1000 m depth in temperate zones (Lagardère, 1977b; Elizalde et al., 1991) and less deep
(300-400 and 800 m) in boreal waters (Mauchline, 1986; Fosså & Brattegard, 1990) of
the North Atlantic. Cartes & Sorbe (1995) noted marked seasonal variations of mysid
abundance on the upper and middle slope, but only very small ones on the lower slope
(>1200 m) of the Catalan Sea (western Mediterranean). Similarly, Sorbe & Elizalde (2013)
found marked seasonal variations in the abundance of suprabenthic mysids on the middle
slope (400 m) off Arcachon (Bay of Biscay, north-eastern Atlantic).
Even fewer Mysida are known to be markedly abyssal. The abyssal plane is preferred
by the family Petalophthalmidae, as indicated by the amazing diversity of the genera
Hansenomysis and Bacescomysis (Birstein & Tchindonova, 1970; Băcescu, 1971b; Lagardère, 1983; Murano & Krygier, 1985). Five species of the genus Boreomysis (Mysidae:
Boreomysinae) were reported in macroplankton and micronekton samples taken at depths
between 1900 m and 5430 m in the north-eastern Atlantic (Hargreaves & Murano, 1996).
C OASTAL ENVIRONMENTS
Vertical distribution. – Most marine mysids are neritic or littoral. Many species are
found in intertidal rocky pools or soft-bottom pools (e.g., Praunus flexuosus, certain
Leptomysis and Paramysis). Many neritic species stay a few or up to tens of meters
above the bottom for most of the day. Depth is certainly not the sole factor influencing
their distribution. For example, during the day in waters off Arcachon, Schistomysis
spiritus lives mostly at 50-100 m above the bottom, the upper 50 cm of which is
always sandy-muddy (San Vicente & Sorbe, 1995). In contrast, a study of night surface
plankton supported by sonar bathymetry in the Tyrrhenian Sea (western Mediterranean;
Ariani & Spagnuolo, 1976) showed — for nine species of Siriellinae and Gastrosaccinae
— distribution patterns according to depth but not related to sandy or rocky types of
substratum. In many species, the vertical distribution varies with the time of day and/or
photic brightness in the context of migratory activity (cf. above, ‘Migration’). In a Baltic
population of Neomysis integer, body size increases with depth and decreases with in
situ daytime light. According to Ogonowski et al. (2013b) size variations with depth are
better related to light intensity than to temperature. From this they concluded that the size
variations observed in Neomysis integer are a response to predation rather than to sizerelated thermal preferences.
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Substrate relations. – In general, the coastal marine and brackish-water Mysida are
benthopelagic or benthic during daytime. These species show substrate relations to
different degrees, visible by many biological features such as body colour, migration,
feeding, social behaviour, etc. (e.g., Clutter, 1969; Wittmann, 1977, 1978a; Fosså, 1986;
Wooldridge & Webb, 1988; Wooldridge, 1989; Macquart-Moulin & Ribera Maycas,
1995). The bottom type is important for many species that dwell on or above substrates
such as mud, sand, gravel, and stone, or on certain types of vegetation. Most Mediterranean
species of Diamysis are strictly benthic or bentho-planktonic, living in marine to freshwater
environments: during the day they occupy vegetation stands, where they show marked
preferences (Wittmann & Ariani, 2012a) for certain vegetable substrata such as the sea
grasses Posidonia in Diamysis bacescui, Zostera in Diamysis bahirensis, and Cymodocea
in Diamysis cymodoceae. The semi-hypogean Diamysis camassai prefers calcareous rock
coated by microalgae, in this respect resembling the Stygiomysida species Spelaeomysis
bottazzii (see below, ‘Feeding’).
Many taxa of Gastrosaccinae (Mysida) are typically psammophilic and can bury
themselves down to 5 cm deep into the sediment, particularly into the sand of the intertidal
zone upon falling tide. The burrowing Gastrosaccinae are active swimmers for feeding and
propagative activities during the night, and bury themselves into the sand during the day; at
falling tide they may bury themselves or, alternatively, may migrate offshore. The intertidal
zonation, migratory, and burrowing behaviour of Gastrosaccinae are strongly influenced
by tidal and diurnal variations of hydrodynamics, salinity, food availability, and risk of
predation (Băcescu, 1940; Wooldridge, 1989; Webb & Wooldridge, 1990; Nonomura et
al., 2007).
Salinity relations. – Salinity is among the most important ecological factors governing
distribution. As in most aquatic invertebrates, the effects of salinity on osmoregulation,
reproduction, distribution, and survival typically show strong variations with temperature
(Vlasblom & Elgershuizen, 1977; McKenney, 1996; Greenwood, 2007; Hanamura et al.,
2009; Paul et al., 2013). Many littoral Mysida are stenohalobious (stenohaline), never
found in estuaries or in seas with low salinity. By contrast, there are also more or less
euryhalobious (euryhaline) species (Stammer, 1936), whose populations are found from
the open sea to estuaries and distinctly brackish lagoons. Certain populations attain enormous densities in ‘marine’ waters influenced by the influx of fresh water, as exemplified
by several Black Sea populations of Paramysis and Mesopodopsis (Băcescu, 1940; Gomoiu, 1978). Most brackish-water species penetrate into the sea but only few of them
into freshwater reaches. In Catalan populations of the essentially marine Gastrosaccus
sanctus, all age stages can migrate up to the mixing zone between infiltrating seawater
and subterranean fresh water (Delamare-Deboutteville, 1955). Within the family Mysidae,
most species of the subfamily Rhopalophthalminae inhabit brackish waters, particularly
estuaries of tropical to subtropical zones. Nonetheless, most brackish-water and almost all
freshwater mysids belong to the subfamily Mysinae. An almost paradoxical case is that of
the Mediterranean Diamysis bahirensis (Mysinae), long considered extremely euryhaline,
with records attributed to populations from metahaline to fresh waters. Recently, however,
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this taxon was split into several species with more restricted ecological ranges (Wittmann
& Ariani, 1998, 2012a, b; Ariani & Wittmann, 2000, 2002). A very wide salinity range of
S = 2.6-65 was recorded in situ for the (sub)tropical Mesopodopsis africana from estuaries
in South Africa (Carrasco & Perissinotto, 2011a).
Other environmental factors. – Food availability as a primary factor of distribution
is expressly or (in)directly treated in various (sub)sections of the present contribution.
Other important ecological factors are oxygen content, particularly in brackish-water
species, along with pH and water movement. The latter determines the re-suspension
of food particles — an important factor for the establishment and maintenance of dense
mysid populations (Clutter, 1967). High silt levels in the water, however, may negatively
affect feeding rate and health and may increase mortality in laboratory-kept Mesopodopsis
africana (cf. Carrasco et al., 2007).
Home site preference and homing behaviour. – Certain Mysidae show some degree
of permanence at their home site, suggesting a clear preference for a distinct biotope
(Clutter, 1969; Wittmann, 1977; McFarland & Kotchian, 1982; Hahn & Itzkowitz, 1986;
Twining et al., 2000). The main investigations in this respect were performed on Mysidium
gracile, whose swarms usually live in association with damselfish or Diadema urchins, but
were also rarely found in other biotopes such as bare sand or Thalassia sea grass (Hahn
& Itzkowitz, 1986). After nocturnal dispersal, marked specimens of Leptomysis lingvura
showed a daily return rate of 0-93%, mainly related to the number of swarms at suitable
microhabitats in the surroundings (Wittmann, 1977, 1978a). Similarly, 77% of the radiolabelled specimens from one swarm of the coral reef mysid Mysidium gracile returned
to the same microhabitat in a single experiment by Twining et al. (2000). As shown by
displacement tests (Hahn & Itzkowitz, 1986), the home site permanence may vary widely,
but certain mysids nonetheless have definite habitat preferences as well as clear homing
abilities.
G ROUNDWATER AND CONTINENTAL ENVIRONMENTS
Groundwater. – Both Stygiomysida genera so far known, Spelaeomysis and Stygiomysis, are found in fresh to brackish water, rarely marine, mostly in groundwater habitats,
almost always near the coast (Caroli, 1924, 1937; Fage, 1924; Villalobos, 1951; Gordon,
1960; Pillai & Mariamma, 1964; Băcescu & Orghidan, 1971; Bowman, 1973, 1976; Pesce,
1976a, b; Pesce et al., 1978; Ariani, 1981c, 1982; Bowman et al., 1984). Most species from
Central America and the Caribbean were recorded from freshwater wells or from freshwater strata in anchihaline habitats (Bowman, 1973, 1976; Bowman et al., 1984; Wagner,
1992; García-Garza et al., 1996; Kallmeyer & Carpenter, 1996). Often no detailed data on
salinity are available, particularly at the sampling depths in habitats with stratified salinity.
At least four species — Spelaeomysis cardisomae, Spelaeomysis cochinensis, Stygiomysis
hydruntina, and Stygiomysis ibarrae — are known only from brackish to marine waters
(Bowman, 1973; Pesce, 1985; Panampunnayil & Viswakumar, 1991; Ortiz et al., 1996; Inguscio, 1998). Spelaeomysis bottazzii from coastal groundwater habitats in south-eastern
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Italy is very rarely found below S = 2 (Ruffo, 1957; Pesce et al., 1978; Ariani & Wittmann,
2010). The estimate by Porter et al. (2008) that 12 out of the 16 currently known Stygiomysida species may have invaded “inland” waters (S = 0-3) reflects mainly the oligohaline range (S 0.5) corresponding to coastal rather than inland groundwater. We agree
with Ruffo (1957) that the two genera are essentially marine (“thalassoid”) Tethyan faunistic elements that invaded the groundwater through the marine-brackish interface (see
also below, ‘Historical biogeography’).
When studied in detail, and under experimental conditions, the animals may show
preference for higher salinity than expected from sampling in shallow groundwater alone.
This may reflect the fact that the animals also often have access to the generally more saline
deep groundwater through underground connecting paths. A three-year study on a natural
population of Spelaeomysis bottazzii in a superficial brackish-water well in south-eastern
Italy yielded a salinity range of S = 2.3-7.1 and seasonal temperature variations of 9.821.6°C (Ariani & Wittmann, 2010). Females taken from the same well, acclimatized in the
laboratory over one month at S = 7.0-7.5, and 16-18°C, consistently chose higher salinities
(S = 9-10; Cesaro et al., 1984) and temperature (21-22°C; Ariani et al., 1984) during
subsequent preference experiments in the laboratory. In line with the hydrogeological
situation of the sampling locality (Ariani, 1982), the chosen values correspond to those
prevailing in deep groundwater (Cotecchia, 1977; Cotecchia et al., 1978). This is where
the animals probably breed and develop, unlike the superficial groundwater where they
dwell mainly for feeding (Ariani & Wittmann, 2010).
Most species of Stygiomysida are cavernicolous or phreaticolous, showing reduced
eyes of which the cornea is reduced to a small number of ommatidia or completely missing
(Caroli, 1924, 1937; Fage, 1925; Villalobos, 1951; Gordon, 1960; Pillai & Mariamma,
1963; Băcescu & Orghidan, 1971; Ingle, 1972; Bowman, 1976; Bowman et al., 1984).
Well-developed or vestigial eyestalks are present throughout. This pattern is also found
in the comparatively small number of cavernicolous Mysidae (Mysida), mostly belonging
to the subfamilies Mysinae and Heteromysinae (Creaser, 1936; Stammer, 1936; W. M.
Tattersall, 1951; Băcescu & Orghidan, 1971; Ledoyer, 1989). Remarkably, certain species
of Hemimysis constitute the dominant faunistic element in dark submarine caves of
the Mediterranean and the north-eastern Atlantic (Ledoyer, 1989; Breton et al., 1995).
These species do not show particular adaptations to this habitat and, notably, have welldeveloped eyes. Accordingly, they are not completely dependent on this habitat, but leave
their caves during the night to feed and then return in the morning. Unlike the noncavernicolous Leptomysis lingvura, the cavernicolous Hemimysis speluncola shows a very
marked negative phototaxis (Macquart-Moulin, 1979; Bourdillon et al., 1980; MacquartMoulin & Passelaigue, 1982; Passelaigue & Bourdillon, 1986; Passelaigue, 1989). Unlike
certain non-cavernicolous species, the photophobia of Hemimysis swarms on the bottom
of submarine caves does not appear to be related to reproduction.
Fresh water. – Freshwater species are dominated by the genus Mysis in boreal
to Subarctic waters of the circum-arctic region, by Taphromysis in the Mid-Atlantic
drainage of America, Diamysis in the Mediterranean, Paramysis in the Ponto-Caspian,
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and Neomysis in inland waters of Japan. Several species penetrate more than 1000 km into
river systems. Only few potamophilous species are so far known from Africa and South
America.
Locomotion, orientation, and taxis
In the Lophogastrida, swimming is mainly effected by the beats of the pleopods, which
are well developed in both sexes. At least in the lophogastrid Gnathophausia ingens, also
the oar-like beats of the thoracic exopods help propelling the body forward (Hessler,
1985). In Mysida, the pleopods are rudimentary in the females and often also in males.
Both sexes swim by the rotating movements of the thoracic exopods. The legs work in
a synergistic fashion, also producing the respiratory current together with filtration
currents (Schabes & Hamner, 1992).
Swimming by thoracic exopods appears to have developed secondarily. All three orders
considered here normally maintain a horizontal, often slightly inclined, orientation of
the body when swimming. A number of Mysidae, particularly species of Praunus and
Limnomysis, often hover with slightly inclined vertical orientation of the body axis. In the
Mysida and Stygiomysida, the thoracic endopods are to some extent used for crawling
and/or holding onto the substrate. During daytime, most littoral Mysidae do not swim
actively; they remain in contact with the substrate and may hover among algae or gravel.
Some species bury themselves shallowly in soft sediment. During the night, all littoral
species show stronger swimming activity and many of them tend to rise up from the
bottom. Foxon (1940) argued that this behaviour reflects negative geotaxis, which turns to
positive geotaxis during light hours. Some species show daytime activity and may continue
to swim in bright sunlight.
The locomotive orientation of the Mysida is conditioned by three types of reflexes:
responses to gravity and inertia mediated by the statocysts, dorsal light reaction (in certain
species) mediated by the eyes, and finally a general position reflex of still unknown nature.
Bainbridge & Waterman (1957, 1958) studied the locomotive orientation in polarized
light. Statistically, Mysidium gracile adjusts its longitudinal body axis perpendicular to the
plane of polarization. This reaction is more distinct in turbid water (Waterman, 1960).
The orientation of certain species may also reflect variations in hydrostatic pressure
(Rice, 1961; Knight-Jones & Morgan, 1966). At the same time, there are reports of an
escape reflex, occurring when the animal becomes attacked, when the water shows sudden
agitation, or when the illumination suddenly changes. Under these conditions, the pleon
is withdrawn under the thorax and then immediately straightened; this induces powerful
backward jumps by tail flipping, which may even project the animal out of the water.
Migration
Seasonal migration. – The seasonal migratory rhythms vary between species and
are mostly synchronized with the period of gonad development and sexual activity —
both of which are strongly affected by temperature and probably also by the photoperiod.
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The Mysida normally do not show large-scale horizontal migrations, but seasonal
shifts in distribution often occur at an intermediate scale: According to Băcescu (1940),
Mesopodopsis slabberi is quite common during the cold season in ‘marine’ waters along
the Black Sea coast of Romania. Here the densities become very low in summer, whereas
in that same season densities strongly increase in the oligo- to mesohaline waters along
the shores near the mouth of the Danube River and in brackish ponds and lagoons. Along
these Black Sea coasts, Paramysis pontica approaches closer to the shore in winter, while
several fluvio-lacustrine species show a wider dispersion with more upstream limits in the
rivers. In the Bay of Biscay, Schistomysis spiritus lives close to the beach in summer but
more distant from the shore at maximum depths of 30-90 m during the rest of the year (San
Vicente & Sorbe, 1995). W. M. Tattersall (1939) observed seasonal shifts in the occurrence
of 19 species off Plymouth (north-eastern Atlantic) and attributed these to horizontal and/or
vertical movements. A number of species are to some extent passively shifted by currents
to localities where they may have little chance of long-term survival (Künne, 1937, 1939).
Diurnal migration. – Some coastal species perform diurnal inshore and offshore
migrations (Debus et al., 1992; Macquart-Moulin & Ribera Maycas, 1995), often related
to water movement and food availability (Webb et al., 1988; Wooldridge, 1989; Webb
& Wooldridge, 1990). Passive or active, diurnal horizontal shifts appear to be a common
feature in populations living in estuaries, fjords, and in the surf zone and other coastal
habitats (Välipakka, 1992; Beyst et al., 2001; Jumars, 2007). A number of Mediterranean
species disperse mainly horizontally in layers close to the sea bottom at night (Wittmann,
1977, 1982). Hemimysis speluncola performs nocturnal inward and outward migrations
from submarine caves, mainly for outside feeding during the night and for inside hiding
during the day (Macquart-Moulin & Passelaigue, 1982; Passelaigue & Bourdillon, 1986;
Passelaigue, 1989; Riera et al., 1991; Rastorgueff et al., 2011).
Detailed studies of diurnal vertical migration were conducted by Russel (1925, 1931),
Fage (1932, 1933), Beeton (1958, 1960), Herman (1963), Macquart-Moulin (1973b,
1975), Toda et al. (1983b), Jumars (2007), and Ogonowski et al. (2013a). Many marine
to freshwater Mysida remain at or close to the bottom during the day, and migrate upwards
mainly for feeding during the night (Grossnickle, 1979; Kouassi et al., 2006). In most cases
the nocturnal migrations result in a wider dispersion within the water column (Toda et al.,
1983b; Apel, 1992; Jumars, 2007). These vertical migrations, most often of endogenous
origin, are synchronized by temporal variations in brightness (Macquart-Moulin, 1973a).
In Mysis relicta and Mysis diluviana this periodicity is influenced by varying conditions
of brightness but also of temperature and possibly even pH. The effects of temperature
variations on this phototropism are sufficient to explain the diurnal and seasonal vertical
migrations of juveniles of various marine coastal Mysidae (Fage, 1932). Geotaxis and
the effects of temperature on geotaxis may also play a role (Foxon, 1940; Bourdillon
& Castelbon, 1983). According to Ogonowski et al. (2013a), the Baltic species Mysis
salemaai shows two subsets of the population: one group shifts upwards in the pelagic
zone and the other remains near the bottom at night. The two migratory strategies are
consistently coupled with diet differences, with pelagic mysids having a more uniform
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and carnivorous diet. Sequencing of mitochondrial genes revealed differences between
geographical locations but not between the subsets predisposed for different migratory
activity (Ogonowski et al., 2013a).
Waterman et al. (1939) studied the nocturnal vertical migrations of several bathypelagic lophogastrids (Eucopia) and mysids (Boreomysis microps) from waters off the
north-western Atlantic coast. The amplitude of daily shifts is on the order of 400 m and
may reflect variations in light intensity, even though the intensity is low at these depths
(200-1200 m). In the north-eastern Atlantic, the lophogastrids Gnathophausia and Eucopia
show much more restricted nocturnal vertical migrations (Hargreaves, 1985).
Tidal migration. – The tidal migrations of Gastrosaccus psammodytes at high-energy
beaches in South Africa may have endogenous components in addition to the obvious
external ones (McLachlan et al., 1979). In order to minimize seaward flushing by tidal
currents in a South African estuary, Gastrosaccus brevifissura employs several strategies,
including utilization of flood-currents, to maximize up-estuary transport (Schlacher &
Wooldridge, 1994). Several littoral species, such as Praunus flexuosus and Schistomysis
spiritus, show a nearshore drift with the tides during very dark nights (Elmhirst, 1931,
1932).
Ontogenetic migration. – Ontogenetic migrations were demonstrated for a number
of pelagic and benthic mysidaceans. A frequent pattern is that juveniles migrate to surface
layers at night while adults remain close to the bottom (Almeida Prado, 1973). As an
inverse example, adult Mysis relicta tend to live in deeper areas than juveniles during the
day in two freshwater lakes in north-east Germany, while the vertical distribution pattern
is apparently inverted at night (Waterstraat et al., 2005). According to Biju et al. (2013),
the numbers of breeding females of Siriella gracilis from tropical offshore waters in the
northern Indian Ocean are not correlated with temperature in the range of 26-31°C, but
significantly increase with salinity in the range of S = 30-37. This is probably due to the
migration to deeper, more saline water layers for selection of the optimal salinity for
embryonic development. The females of the lophogastrid Gnathophausia ingens and the
mysid Mysis stenolepis breed in deeper waters and migrate to more superficial strata prior
to releasing the young (Amaratunga & Corey, 1975; Childress & Price, 1978). An inshore
migration of adults in spring coincided with the onset of reproduction of the overwintering
generation of Americamysis bigelowi in a New Jersey estuary (north-western Atlantic;
Allen, 1984).
Social aggregation
Types of aggregation. – Considerable attention has been focused on the distributional,
behavioural, and physiological aspects of swarming in the Mysida (Clutter, 1967, 1969;
Berrill, 1969b; Macquart-Moulin, 1970, 1971, 1973a, b; Mauchline, 1971; Zelickman,
1974; Wittmann, 1977; O’Brien, 1988; Twining et al., 2000). Definitions of aggregation in mysids by Clutter (1967), Mauchline (1971), and Zelickman (1974) were mainly
related to social interaction. O’Brien (1988) classified grouping according to the mechanisms stimulating their formation and maintenance. Definitions by Wittmann (1977) were
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primarily geometric and, therefore, more practical for comparative field observations on
different species. He considered essentially: inter-individual distance excluding social interaction (dispersion); no or reduced regularity in spatial arrangement (aggregation sensu
stricto); regularity in spatial arrangement (swarms); swimming in the same direction
(schools) [apart from mere effects of water movement]; presence inside a swarm of structures differing in abundance of distinguishable individual types (sub-swarms); presence
of non-dominant species in an association (guests).
Structure of aggregations. – The internal arrangement of mysid and euphausiid
swarms has in common that the individuals avoid positions directly above and below their
neighbours (O’Brien, 1989). Different age groups are often organized in separate swarms
or sub-swarms during the day (Macquart-Moulin, 1970; Wittmann, 1977; O’Brien, 1988;
Ohtsuka et al., 1995). Juvenile sub-swarms of Mediterranean Leptomysis typically stay
closer to the substrate where they are less visible for (bentho)pelagic predators and at
lower risk to be consumed by larger conspecifics. Here, however, they may be exposed to
an increased risk of being attacked by benthic predators, for example by epibenthic gobies
from below (Wittmann, 1978a). Modlin (1990) observed an inverse stratification in the
mangrove mysid, Mysidium columbiae, with the juveniles near surface and the breeding
females near bottom. Based on multifrequency acoustic echo-sounding on three coastal
species, particularly Neomysis rayii, Kaltenberg & Benoit-Bird (2013) concluded that
intra-patch clustering of mixed-size and mixed-species aggregations may greatly affect the
interactions among mysids and their predators. Preferential grouping of sexually mature
individuals is often observed and may represent breeding aggregations (Clutter, 1969;
Mauchline, 1971). Daytime swarming may also help to find mating partners, as suggested
by residual dense aggregations of the Mediterranean Leptomysis lingvura, in which mating
normally starts after sundown, while most of the remaining population is already dispersed
over the sea bottom (Wittmann, 1982).
Cohesiveness of aggregations. – As first noted by Steven (1961), mysid schools
perform cohesive and precise locomotion comparable to that of fish. According to
Zelickman (1974) these patterns are controlled by the combined effects of external
stimuli and collective (inter-individual) responses. Monospecificity and separation of
age groups are controlled by distributional separation such as bathymetric zonation,
substrate-preference, and activity periods. They are also controlled by active avoidance of
individuals of different size and/or preference for same size. Clutter (1969) assumes that
mysids respond mainly to the visual image of their neighbours, but tactile and olfactory
stimuli may also be important. According to Wittmann (1977) several swarming species
are unable to identify others exactly like themselves; there may be some capability for a
general mysid-identification. Cohesiveness of swarms is controlled by preference for the
same habitat and probably by an often non-specific gregariousness.
According to Wittmann’s (1977) investigations, mysids seem to have evolved two
different strategies of optimizing swarm stability and cohesiveness. One (shown by
Mesopodopsis slabberi) is to reduce substrate relations and to intensify social interaction. Such species can form motile, polarized, cohesive groups. The second method (shown
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by Leptomysis lingvura) is to maintain a relatively low level of collective responses and
to intensify habitat-relations such that the population occurs only at a few distinct places
within its area. Such species form non-motile swarms (fig. 54.41A, C) or open near-bottom
aggregations. The motility of swarms may change with season and sexual maturity (Ohtsuka et al., 1995). This second method allows the species to profit from the protection
afforded by the substrate, for example, by means of camouflage and/or by hiding among
vegetation or on the sediment upon predator attack (Wittmann, 1977, 1978a). As a striking
example of substrate relations, the homing behaviour of the demersal tropical mysid Mysidium gracile facilitates swarm reformation each morning after nocturnal dispersal (Twining et al., 2000; see also above, ‘Home site preference and homing behaviour’). In general
agreement with the above concept, the relative inter-individual distances and other indices
of internal swarm structure, as far as examined, vary between substrate-specialized mysids,
non-substrate-specialized mysids, and the again more pelagic euphausiids (O’Brien, 1989).
In most mysid species, the groupings tend to disintegrate and the individuals disperse
over the substrate or in the water column during the night (Macquart-Moulin, 1970,
1973b; Wittmann, 1977, 1978a, 1982; Twining et al., 2000). In laboratory experiments
by Macquart-Moulin (1973b), the test specimens of Leptomysis lingvura dispersed when
luminosity dropped below 1 lux, and reformed swarms above about 30 lux. Nonetheless,
certain species aggregate throughout the night (O’Brien, 1988; Patzner, 2004). In Mysidium columbiae, the adults become solitary at night, whereas the juveniles continue to
form compact swarms (Modlin, 1990).
Benefits and disadvantages of aggregation. – Based on published results, the benefits
of gregariousness for mysids are facilitation of position maintenance, increased reproductive potential, trapping of prey, protection from predators, and energy saving (Clutter,
1969; Mauchline, 1971; Wittmann, 1977; O’Brien, 1988; Modlin, 1990; Ohtsuka et al.,
1995; Ritz et al., 2011). Ritz (2000) showed that cohesive mysid schools consume less
energy for swimming compared to un-cohesive small groups. By measuring oxygen uptake, Ritz et al. (2001) showed that large mysid swarms consume less energy pro capite for
escape responses compared to small swarms and again to solitary specimens. Swarms of
species of Gastrosaccus, Anisomysis, and Tenagomysis aggregate for feeding (Wooldridge,
1989; Ohtsuka et al., 1995). Ritz & Metillo (1998) found, however, no significant effect
of swarming on success of food capture in Paramesopodopsis rufa from coastal waters
of Tasmania. Apparent disadvantages of aggregation are enhanced competition for food,
facilitation of cannibalism, and vulnerability to large predators that could break up swarms
(Emery, 1968; Hahn & Itzkowitz, 1986; Ohtsuka et al., 1995; Johnston & Ritz, 2001).
Heterospecific aggregations. – Mysids are often found in mixed swarms or schools
formed by 2-5 species (Macquart-Moulin, 1970; Wittmann, 1977; Ohtsuka et al., 1995).
The swarms stay mostly (not always) at the habitat usually preferred by the numerically
dominant species. The NE-Atlantic-Mediterranean Leptomysis heterophila got its specific
name from its regular habit to co-occur with other mysid species (Wittmann, 1986a).
Such associations may be mutualistic because potential predators may be confused by
differences in anti-predatory behaviour within the same association. However, such
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associations may be one-sided if the predator is directed to the other mysid species. Several
mysid species tend to prey on larvae and early juveniles of (their own and) other swarming
species (Johnston & Ritz, 2001). Mysid swarms are often associated with sessile benthic
invertebrates (fig. 54.41D; see below, ‘Symbiotic associations’).
In shallow tropical backreef habitats, McFarland & Kotchian (1982) observed two
species of Mysidium to form mixed schools with larvae of the fish Haemulon flavolineatum. These associations break down at night, when both partners disperse for feeding,
and restructure at the same reef each morning. This kind of association has some
mutualistic elements, but appears ambivalent for the mysids, as they may fall prey to the
fish larvae as these grow.
Grooming
Behavioural and SEM-observations by Acosta & Poirrier (1992) showed that the mysid
Americamysis bahia uses specialized setae on the mandibular palps and on the thoracic
endopods 2-8 to clean the body from epizoites and particulate matter. The second thoracic
endopod is the most active in grooming the antennae, setae of the marsupium, and other
thoracic appendages. The eighth thoracic endopods clean the outer face of the marsupium.
The telson and uropods are also cleaned. Prevention of fouling may be particularly
important for the females during the long period when they breed their young and do not
moult (see above, ‘Incubation’). Newly emerged young are poorly equipped with cleaning
setae, suggesting that the higher moult frequency is the main mechanism to counter fouling
in juveniles.
Sets of specialized setae on the terminal segment of the mandibular palp are present in
most species of the family Mysidae. Mauchline (1980) figured such setae for Schistomysis
ornata and interpreted these as components for cleaning the cutting and grinding surfaces
of the mandibles as well as for removing food from the posterior mouthparts and to push
it into the mouth. Combining the observations by Mauchline (1980) and Acosta & Poirrier
(1992) points to an integrative role of the mandibular palp for feeding and grooming.
Food and feeding
Feeding mechanisms. – The feeding mechanisms and digestion were studied in
species of Lophogastrida (Manton, 1928a), Mysida (Depdolla, 1923; Cannon & Manton, 1927a; Băcescu, 1940; Tattersall & Tattersall, 1951; Foulds & Mann, 1978), and
Stygiomysida (Nath & Pillai, 1972a; Ariani, 1982). Feeding is generally based on three
independent, often coexisting procedures:
The first procedure is fragmentation of large to medium-sized, living or dead particles
that are grasped with the thoracic endopods and then held to the mouth with the aid of the
anterior endopods and the mandibular palp. The food is cut into small fragments by the
incisor processes of the mandibles. The fragments are reduced to a very fine pulp by the
molar processes of the mandibles and the internal armature of the stomach. This mode of
feeding was observed in the laboratory in three Mediterranean species of Diamysis when
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fed thin flakes (Tetramin® ) composed largely of dried algae (Ariani, 1966, 1979, 1981b;
Ariani et al., 1982, 1999; Ariani & Wittmann, 2000).
The second procedure, observed in Lophogastrida and Mysida, is the filtration of
fine particles. The filtration current is provided by rotating movements of the thoracic
exopods and by vibrations of the maxillae (Manton, 1928a). Food enters the feeding
basket formed by thoracic endopods and maxillae from the front (Schabes & Hamner,
1992). The particles accumulate in a ‘feeding tank’ anteriorly limited by the paragnaths.
From here they are carried to the mouth or swept away as they arrive at the long setae of the
basal endites of the maxillae and of the first pair of thoracopods. Lucas (1936) calculated
that the mysid Neomysis integer can consume up to 6 million diatoms per hour. This
feeding mechanism is often supported by strong movements of the animal, agitating water
against the substrate. Certain species are exclusively limivorous and strongly perform
this procedure. However, increased silt levels in the water may hinder the food-collecting
ability in laboratory-kept Mesopodopsis africana (cf. Carrasco et al., 2007).
The third procedure is rasping the coat of autotrophic microorganisms from the
substrate surface with the strong mandibles. In the essentially phreaticolous but locally
also cavernicolous Stygiomysida species Spelaeomysis bottazzii (cf. Ariani, 1982; Ariani
& Wittmann, 2010), this mode of feeding was observed in the field at a lighted well and
in the laboratory under both light and dark conditions. The ingested microorganisms were
diatoms, green algae, and Cyanobacteria; the substrate consisted of soft calcareous rock
(Quaternary calcarenite). This is generally in line with the geological characteristics of
the geographical area, where the species is found in caves or wells (Ariani, 1981b, 1982).
When living under lighted conditions, animals accumulate fat reserves as subcuticular fat
bodies. This is visible in a change in body colour from white to pale up to marked yellow.
Both field and laboratory observations showed that Spelaeomysis bottazzii produces
cylindrical faecal pellets consisting mostly of amorphous calcareous grains, rarely with
additional ‘enigmatic’ chains of well-formed calcite crystals (Ariani, 1982). These crystals
might result from unknown processes of dissolving and re-crystallization of calcium
carbonate anywhere in the digestive system. During an observation time of two weeks
in the laboratory, Spelaeomysis bottazzii produced almost equal volumes of faecal pellets
per mm of body length in the presence of only fragments of bare porous rock, compared
to fragments covered by autotrophic micro-organisms. This suggests that the species can
survive during the long incubation period in deep groundwater (Ariani & Wittmann, 1997,
2010) by using the organic matter infiltrated into the porous rock or contained in a fossil
state.
Digestion. – Digestion takes about 2-4 hours in various Mysidae (Benko, 1962;
Fockedey et al., 2005). By contrast, it takes about 12 hours in the cavernicolous Stygiomysida Spelaeomysis longipes (cf. Nath & Pillai, 1972a). In laboratory specimens of
the mysid Neomysis integer, egestion rates as a measure of ingestion generally increased
with increasing temperature and salinity, but were suppressed by the combination of high
temperature and high salinity (Roast et al., 2000). In the laboratory, the faecal pellets of
this species were generally enriched in nitrogen, probably due to bacterial growth on the
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pellets and on the peritrophic membrane, as well as to the disintegration of intestinal cells
(Fockedey et al., 2005).
Certain species, such as Mysis stenolepis, can digest the cellulose of vegetal debris
(Foulds & Mann, 1978) by means of endogenous cellulases (Friesen et al., 1986a).
Niiyama et al. (2012) found cellulase activity in all six mysid species tested from a
mangrove estuary in Malaysia. In three coexisting mysids from the coasts of Tasmania,
Metillo & Ritz (2001, 2003) found differential activity of laminarinase as a measure of
herbivorousness on algae. They also reported differential responses to feeding stimulants
and suppressants, both findings pointing to different partitioning of the feeding niche.
Nature of food. – The nature of the food was studied in species of Mysida (Blegvad,
1915; Depdolla, 1923; Băcescu, 1940; Tattersall & Tattersall, 1951; Mauchline, 1968;
Bowers & Grossnickle, 1978; Grossnickle, 1979; Siegfried & Kopache, 1980; Wittmann
& Ariani, 2000; Hanamura et al., 2012; Hanselmann et al., 2013) and Stygiomysida (Nath
& Pillai, 1972b; Ariani, 1982; Ariani & Wittmann, 2010). Most species are omnivorous,
chasing actively after planktonic larvae and small crustaceans, but also ingesting fragments
of algae and vegetal debris (Bowers & Grossnickle, 1978; Fenton, 1996; Thiel, 1996;
Fockedey & Mees, 2005; Cibinetto et al., 2006; Jumars, 2007; Lehtiniemi & Nordström,
2008; Lehtiniemi et al., 2009).
Analysis of stomach contents and food choice experiments suggest that the mysid
Limnomysis benedeni is essentially herbivorous to detritivorous and probably shows no
major predatory impact on zooplankton in the field (Wittmann & Ariani, 2000; Gergs et
al., 2008; Hanselmann et al., 2013). From stable isotope analysis of an invasive population
of Limnomysis benedeni in a gravel pit lake in the catchment of the Rhine River, Fink
& Harrod (2013) concluded that pelagic food sources prevail at least in eutrophic and
turbid lakes with low benthic primary production. In the laboratory it selects leaf litter
according to factors related to carbon content and polyphenol content; fungal colonization
and conditioning by fungi also play a role (Aßmann et al., 2009). Some mysids feed mainly
on zooplankton (Hansson et al., 1989; Cartes & Sorbe, 1998; Chigbu, 2004; Borcherding
et al., 2006). Certain mysids prey upon eggs and larvae of fish when these are offered in the
laboratory (Tornainen & Lehtiniemi, 2008). Cannibalism is often reported from mysids in
captivity.
Food search and selection. – Crouau (1978a, 1983, 1987, 1989) observed food search
and feeding behaviour in the cavernicolous tropical mysid Antromysis juberthiei. He
described a great variety of chemosensitive and mechanosensitive setae on antennulae,
antennae, and mouthparts, which could be important for detecting, chasing, and grasping
food. According to Metillo & Ritz (1994, 2003), food resource partitioning of three cooccurring species of Mysidae from coastal marine waters of Tasmania is characterized by
differences in gut volume and internal armature of the cardiac region, and by differential
chemosensory feeding behaviour.
Mysids typically have a high capability of adapting their selection of food sources and
feeding behaviour to local environmental conditions and food availability (Johannsson
et al., 2001; Lehtiniemi & Nordström, 2008; Vilas et al., 2008; Fink et al., 2012;
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Hanamura et al., 2012; Marty et al., 2012). A good example is the (sub)tropical, euryhaline
Mesopodopsis africana, which modifies its diet rapidly under natural conditions. In certain
parts of the same South African estuary, it utilizes mostly particulate organic matter, in
another part mainly macroalgae, and again elsewhere copepods (Carrasco & Perissinotto,
2010a, 2011b). Nonetheless, in this estuary it is also an important grazer of microalgae and
its energetic requirements may be met by a microalgal diet alone (Carrasco & Perissinotto,
2010b). In Mysis diluviana from Lake Ontario, its diurnal vertical migration activity
and the resulting nocturnal pelagic versus benthic feeding vary with the season, mainly
according to the availability of diatoms (Johannsson et al., 2001). The high plasticity
of food selection may be a major obstacle in transferring laboratory results to the field.
Fink et al. (2012) observed selective feeding of Limnomysis benedeni on two Daphnia
species in the laboratory and in outdoor mesocosm experiments, but Wittmann & Ariani
(2000) and Hanselmann et al. (2013) found no correspondence in stomach contents of
field animals. According to field studies by Borcherding et al. (2006) on Hemimysis
anomala, the proportion of zooplankton consumed is higher during the nocturnal stay
in more superficial water layers compared to daytime dwelling on the bottom. Cartes &
Sorbe (1998) found strong depth patterns in three marine deep-water species of mysids:
the relative amount of phytodetritus versus pelagic food in the stomachs increased with
depth. Zooplankton clearance rates of freshwater Mysis in the laboratory did not vary
with time of day, light intensity or temperature (Cooper & Goldman, 1982), suggesting
that the differences observed in nature to some degree reflect different prey density at
different water depths during vertical migration. Light has a negative effect on predation
rates in laboratory specimens of the marine littoral mysid Gastrosaccus roscoffensis, which
in nature tends to bury itself a few centimetres into the sediment during the day (Escánez
et al., 2012). In a freshwater population of Hemimysis anomala, Borcherding et al. (2006)
reported that small specimens feed relatively more on phytoplankton, large ones more
on zooplankton. In line with this, a stable nitrogen isotope study by Branstrator et al.
(2000) provided evidence for increasing zoophagy with increasing body size and maturity
in freshwater populations of Mysis diluviana. By contrast, Fockedey & Mees (2005) found
no qualitative differences in diet according to sex or developmental stage in the omnivorous
estuarine mysid Neomysis integer.
Adaption to food scarcity. – The hypogean Stygiomysida Spelaeomysis longipes
counters the food scarcity in subterranean environments by feeding on decaying vegetable
matter, as observed in a well with a supply of plant material (Nath & Pillai, 1972b).
A different strategy is shown by the hypogean Spelaeomysis bottazzii and the semihypogean mysid Diamysis camassai, which exhibit micro-phytophagy in or near the
margins of the photic zone during part of their life cycle. Both species show a strong
mandibular apparatus capable of scratching microorganisms from hard substrate. This
appears to be an important prerequisite for life in deeper, dark groundwater, to which
the females may escape from predation by epigean animals when incubating their young
(Ariani & Wittmann, 2002, 2010).
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Trophic interactions
According to Chigbu (2004), the mysid Neomysis mercedis feeds selectively on Daphnia and can control the abundance of this cladoceran in Lake Washington. Populations
of several cladocerans were diminished by intentional or non-intentional introductions of
Mysis relicta and Hemimysis anomala in European lakes and impoundment basins (Langeland, 1981; Fürst et al., 1984; Koksvik et al., 1991; Langeland et al., 1991; Ketelaars et al.,
1999). The frequency of predation by two Mysis species on the cladoceran Cercopagis
pengoi in the laboratory was consistently higher in juveniles than in adults, and in Mysis
mixta higher than in Mysis relicta (cf. Gorokhova & Lehtiniemi, 2007). Both species adjust
their feeding behaviour under the risk of predation by fish (Lehtiniemi & Lindén, 2006).
The predatory mysid Rhopalophthalmus terranatalis controls the density of the mysid
Mesopodopsis wooldridgei in a South African estuary by feeding on the juveniles of the
latter species (Wooldridge & Webb, 1988). Three mysids are involved in trophic interactions in the Guadalquivir Estuary (south-western Spain), where the more carnivorous
Rhopalophthalmus tartessicus and the more omnivorous Neomysis integer compete for
feeding on juveniles of the more micro-herbivorous Mesopodopsis slabberi and on copepods (Vilas et al., 2008). A predator-prey relationship between various species of mysids
is also suggested by laboratory data on Praunus flexuosus as a predator of small specimens
of Neomysis integer from a North Sea estuary (Winkler & Greve, 2004).
Seasonally increased predation pressure of grey whales on the dominant mysid species
along the coast of British Columbia (north-eastern Pacific) favours the propagation of
subdominant species. This is an example for elevated species diversity being supported
by top-down control (Feyrer & Duffus, 2011).
Symbiotic associations
Diversity of symbiotic relationships (fig. 54.41). – Many Mysidae (Mysida), particularly species belonging to the Heteromysinae genera Heteromysis (fig. 54.41B) and Ischiomysis (fig. 54.41D), show associations with benthic invertebrates such as sponges,
madreporarian corals, sea anemones, sabellids, pagurids, and ophiuroids (Bonnier & Pérez,
1902; W. M. Tattersall, 1922; Clarke, 1955; Pillai, 1968; Băcescu, 1970, 1976; Băcescu
& Bruce, 1980; Ortiz & Gomez, 1988; Vannini et al., 1993; Wirtz, 1997, 2009; Williams
& McDermott, 2004; Wittmann, 2008, 2013a). Heteromysis harpax is usually found as a
family group formed by a pair of adults together with juveniles in shells inhabited by Dardanus hermit crabs (Vannini et al., 1993). These mysids probably identify suitable shells
by visual and chemical cues and avoid other species of hermit crabs. Among species of
the subfamily Mysinae, Idiomysis tsurnamali is associated with jellyfish (Băcescu, 1973a;
Chadwick et al., 2008; Niggl & Wild, 2009), Idiomysis inermis with sea anemones (Greenwood & Hadley, 1982), and Anisomysis levi with gorgonians (Băcescu, 1973b). Swarms of
several Mediterranean species of Leptomysis (Leptomysinae) show rather loose, transient
associations with the sea anemones Anemonia viridis (fig. 54.41C) and Aiptasia mutabilis
(Wittmann, 1977, 1978a, 1982, 1986b; Patzner & Debelius, 1984; Patzner, 2004). Swarms
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Fig. 54.41. Associations between Mysidae (Mysida) and sessile benthic invertebrates. A, swarm of
Leptomysis sp. A at the long-spined sea urchin Diadema antillarum Philippi, 1845, from Madeira,
mysids facing water current; B, adult female Heteromysis sp. inside open fan of the sabellid worm
Branchiomma nigromaculatum (Baird, 1865) from Cape Verde Islands; C, swarm constituted mainly
by breeding females of Leptomysis lingvura marioni Gourret, 1888, above the snakelocks anemone
Anemonia viridis (Forskål, 1775) from the Gulf of Naples; D, dense aggregation of undetermined
Mysidae above oral disk of the club-tipped anemone Telmatactis cricoides (Duchassaing, 1850)
from Trindade, a small island in the tropical south-west Atlantic. [A, after Wirtz, 1995; B, photo
Peter Wirtz; C, after Wittmann, 1978a; D, after Wittmann, 2013a (photo Lisandro de Almeida).]
of Leptomysis, Mysidium, and other genera may show facultative associations with sea
urchins (fig. 54.41A; Randall et al., 1964; Wirtz, 1995; Wittmann & Wirtz, 1998).
Diurnal periodicity of symbionts. – In southern France, Patzner (2004) observed
Leptomysis lingvura to remain at the anemones over night. In shallow water of the northern
Adriatic Sea, Wittmann (1977, 1978a) observed that swarms of this and several other
species of Leptomysis disintegrate during the night and re-gather in the morning over
various types of substrates, including substrates other than anemones (see above, ‘Habitat
and distribution’). Inverse periodicity may also be shown, e.g., by a so far un-described
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Heteromysis species from the Cape Verde Islands, which is closely associated with the
sabellid annelid Branchiomma nigromaculatum only during the night (fig. 54.41B; Wirtz,
2009).
Antipredator behaviour by symbiosis. – Some direct observations on mysids underline
the role of symbiosis as antipredator adaptation. According to Băcescu (1973a),
Idiomysis tsurnamali hovers in swarms above the jellyfish Cassiopea and hides between
the tentacles when potential predators approach. Heteromysis actiniae swims closely
around the tentacles of the anemone Bartholomea annulata and may rest on the basis of
the tentacles, where nematocysts are less dense (Clarke, 1955). As far as observed, other
Mysidae associated with cnidarians avoid physical contact with their host. Upon approach
of predators from the side or from above, swarms of several species of Leptomysis swim
closer to whatever type of substrate is available, including sea anemones, but do not seek
shelter between tentacles; the mysids are killed upon forced physical contact with the
nematocysts (Wittmann, 1978a). Mysidium gracile and a few other species of Mysidae
seek shelter between the spines of sea urchins when threatened (Randall et al., 1964).
In coral reefs of Florida, Mysidium gracile shows a facultative association with nesting
pomacentrid fish. Upon approach of predators, the mysids actively crowd into the nest cave
defended by the pomacentrid (Emery, 1968).
Commensalism. – A commensal relationship between mysids and their hosts is
often assumed, but only few direct observations are available. Heteromysis harpax feeds
on suspended particles and plankton; apparently it does not clean its hermit crab host
and does not feed on the host’s faeces (Vannini et al., 1994). By contrast, Heteromysis
actiniae does feed on the faeces expelled by its sea anemone host (Clarke, 1955). Niggl
et al. (2010) showed by stable element labelling experiments that the symbiotic mysid
Idiomysis tsurnamali feeds on organic matter other than faeces released by its jellyfish
host Cassiopea. It clearly consumes organic matter derived from mucus released by the
jellyfish.
Parasites
Several Lophogastrida and Mysida were found to be affected by epibionts or even
by true external or internal parasites. Their integument may be colonized by algae
and protists (Hoenigman, 1960). Several species of Peritrichia and Apostomida (phylum
Ciliophora = Ciliata) are of major importance among the epizoites (i.e., not ‘epizooties’)
(Hanamura & Nagasaki, 1996). The ciliates appear to be capable of re-attaching rapidly
on the fresh cuticle after moulting of the host (Ohtsuka et al., 2006). Prevalence of
the vorticellid Zoothamnium duplicatum as an epibiont on the cuticle of the mysid
Mesopodopsis orientalis is negatively correlated with salinity in a mangrove estuary
in Malaysia (Hanamura et al., 2012). True ectoparasites are mainly represented by
crustaceans, namely at least three species of nicothoid copepods, and a number of
epicarideans (Isopoda, currently in the suborder Cymothoida, families Asconiscidae and
Dajidae). The latter are mainly present in the marsupium, occasionally also on the carapace
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or the pleon (Nouvel, 1951). Nicothoid copepods and epicaridean isopods show marked
effects on the population dynamics of several mysids by infesting the marsupium (Daly &
Damkaer, 1986; Ohtsuka et al., 2006). The leech Mysidobdella borealis sucks on the body
fluid of its mysid hosts (Utevsky & Sorbe, 2012). According to field and laboratory studies
by Allen & Allen (1981), recruitment and survival of this Boreoarctic leech are determined
at the southern range of its distribution by water temperature and by the seasonal onshoreoffshore migrations of its main host, the mysid Neomysis americana. The externally
established Ellobiopsidae (phylum Myzozoa) implant a fixation organ into the tissue of the
host in order to suppress moulting and to modify the development of secondary sexual
characteristics (Coutière, 1911; Fage, 1936; Nouvel, 1941, 1954; Nouvel & Hoenigman,
1955; Vader, 1973). This may induce castrating and/or feminizing effects on males
(Ohtsuka et al., 2003, 2006). Reports of endoparasitism regard: microsporidians (Mercier
& Poisson, 1926); metacercariae of the trematode Bunocotyle cingulata (cf. Popova &
Nikitina, 1972); larvae of the cestode Amphilina foliacea, whose adults infest sturgeons;
first larvae of the nematode Anisakis simplex, whose second larva infests marine fish and
whose final stage infests marine mammals (Makings, 1981); larvae of the acanthocephalan
Echinorhynchus leidyi, which infest freshwater fish as definitive hosts (Prychitko & Nero,
1983).
ECOLOGICAL AND ECONOMIC IMPORTANCE
Contribution to biodiversity
Global diversity. – Based on a thorough evaluation of potential synonymies in 2012,
a total of 1195 described extant species in 182 genera were confirmed for the orders
Lophogastrida, Stygiomysida, and Mysida (see below, ‘Classification’). This is 1.8% of the
total of 66 914 extant crustacean species reported by Ahyong et al. (2011), who somewhat
overestimated the numbers of described mysidaceans by indicating 1247 species. More
conservative estimates of global species numbers were provided by Schram (2013), who
indicated 1141 mysidaceans [data on orders pooled by us] and only 49 658 crustaceans.
Wittmann (1999) documented a more than linear but less than exponential increase of
numbers described since 1860, and extrapolated a minimum number of around 4000 living
species of mysidaceans. In rough accordance with this, Appeltans et al. (2012) estimated
1180 accepted plus 2090-4120 so far unknown species of marine Mysida, yielding a
figure of 3270-5300 living marine species (not including continental species). The trend of
descriptions is not homogeneous and currently mainly reflects benthic and benthopelagic
species, whereas first descriptions of pelagic species are slowing down (Wittmann, 1999).
The fraction of pelagic species among total numbers known peaked at 42% in 1910 and
decreased to about 20% in 2012. Most species are strictly marine. Porter et al. (2008)
estimated that “inland” species (S = 0-3) represent only 6.7% of “mysid” (i.e., Mysida plus
Stygiomysida) diversity and are concentrated in the Palaearctic and Neotropical regions.
As indicated below (‘Ecological biogeography’), only about 5% live at least partly in fresh
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water (S = 0-0.5), with the hotspot of diversity in the Ponto-Caspian region. Numbers
of described mysidacean species show a distinct peak at 30-40°N, with a sharp decline
towards polar regions (Wittmann, 1999). The strong hemispherical asymmetry may
reflect a major bias in the degree of research effort. In fact, a globally more symmetrical
distribution pattern is obtained by expressing diversity as the number of species per
1000 individuals sampled with epi- to hyperbenthic nets in shelf areas. However, some
asymmetry may have natural causes in as far as there are more extended shelf areas in the
Northern Hemisphere.
Regional and local diversity. – Many species of Lophogastrida are meso- to bathypelagic with a widespread, often transoceanic distribution. Price et al. (2009) listed nine
species for the Gulf of Mexico, eight of which show a panoceanic distribution; only one
is restricted to the western Atlantic. Wittmann & Riera (2012) listed twelve species from
waters off eastern Atlantic islands: ten of these are panoceanic, one is endemic to the
Atlantic Ocean, and another endemic to the eastern Atlantic. There are no lophogastrids in
the Arctic ocean and only a few species in the Antarctic. San Vicente (2010b) listed only
panoceanic species, namely two Gnathophausiidae and one Eucopiidae, for waters south
of 60°S. Unsurprisingly, there is a strong latitudinal gradient in the Southern Ocean, as
suggested by a total of eight species, including two Lophogastridae, in the Subantarctic
region, which is only fuzzily defined by the Subtropical Convergence as its northern limit.
Compared with Lophogastrida, a much higher diversity and degree of endemism are
found in Mysida, mainly due to a larger fraction of benthopelagic and benthic species.
San Vicente (2010b) reported 34 species from Antarctic and 52 from Subantarctic waters.
Petryashov (2004) indicated 28 species for the Euro-Asiatic sub-basin of the Arctic Basin
and adjacent seas. Price & Heard (2009) listed 52 species for the Gulf of Mexico, 13
being endemic. Striking hotspots of endemism are found in continental and semi-enclosed
‘seas’: Petryashov & Daneliya (2006) documented 21 Mysidae for the Caspian Sea,
all belonging to the flock of Ponto-Caspian endemics. Skolka (2005) listed 20 species
from coastal waters of the western Black Sea, mainly Ponto-Caspian endemics but also
several species derived from Mediterranean immigrants. San Vicente (2010a) indicated
37 endemics (39%) among a total of 95 species in marine waters of the Mediterranean
Sea. High levels of molecular diversity within and between populations of Mesopodopsis
slabberi in the Mediterranean and north-eastern Atlantic (Remerie et al., 2006) suggest a
high additional (cryptic) diversity in the Mediterranean.
Most Stygiomysida show a subterranean mode of life in an- to (mixo)euhaline waters
including anchihaline groundwater, caves, and wells of subtropical to tropical zones. All
seven species of Stygiomysis and seven out of the nine species of Spelaeomysis currently
known are stenoendemic to karstic coastal waters within very restricted areas. Eleven
out of these 16 species make an important contribution to the amazing subterranean
biodiversity of Mexico and the Caribbean. Only Spelaeomysis cardisomae shows a wider
distribution range, being found in small pools at the bottom of crab burrows in the
Caribbean as well as along the coast of Peru (Bowman, 1973).
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Environmental change and biodiversity. – Anthropogenic range expansion of certain
biota is among the most important drivers of environmental change. Potentially detrimental effects of anthropogenic species introductions are discussed below (‘Impact of
bioinvaders’). According to Aladin et al. (2006), the unique fauna, including 20 endemic
Mysidae, of the Caspian Sea is endangered by negative impacts from river flow control,
poaching, water level fluctuations, pollution, exotic species, and climate change. Compared with the state of knowledge in 1930, Wittmann (2001) counted increased species
numbers in the peripheral islands and submarine banks of the Gulf of Naples, probably
due to intensified faunistic research. By contrast, there was a strong decrease in species
numbers in the inner parts of the gulf, probably due to human impact on freshwater input,
disappearance of brackish waters and fresh waters by drainage and canalization, and by
pollution leading to eutrophication of coastal waters and impoverishment of the benthos.
Chevaldonné & Lejeusne (2003) documented the range expansion of Hemimysis margalefi
and the corresponding regression of the cold-water congeneric Hemimysis speluncola in
marine caves of the Mediterranean and attributed this to regional warming. These processes appear to be part of a general trend of ‘tropicalization’ of the Mediterranean marine
flora and fauna. This is linked to climate change and invasion of warm-water biota due
to anthropogenic introduction and via immigration across the Suez Canal and the Strait of
Gibraltar (Bianchi & Morri, 2000; Bianchi, 2007). In a wider context, Coll et al. (2010) observed a general decreasing trend in biodiversity from west to east and north to south in
the Mediterranean Sea, linked with habitat loss and degradation, pollution, climate change,
over-exploitation, and invasive species.
A counter-balance of potential benefits and damage suggests, that negative effects
of human-driven environmental change appear to strongly prevail over positive effects.
Due to current global threats to biodiversity, there is reasonable concern that current
adverse trends involving human impact could already wipe out a substantial portion of
the estimated minimum of 4000 mysidacean species before they have been described by
science (Wittmann, 1999).
Impact on ecosystems
Role as environmental engineers. – In marine ecosystems, diurnally migrating mysids
represent important trophic linkages between pelagic and benthic food webs by being
predators and prey in both habitats (Jumars, 2007). The role of mysidaceans in transforming microplankton, detritus, and debris into animal matter is far from being negligible
(Thiel, 1996; Lehtiniemi & Nordström, 2008). Mysid grazing activity can significantly
affect the survival and settlement of kelp zoospores (VanMeter & Edwards, 2013). The
roles of the invasive mysid Limnomysis benedeni in leaf litter decomposition (Aßmann et
al., 2009) and in biosynthesis of polyunsaturated fatty acids (Fink, 2013) in freshwater
ecosystems are discussed in the next paragraph below. In the Gulf of Finland, the least
saline part of the Baltic Sea, two pelagic Mysis species increase the total chlorophyll-a
concentration of phytoplankton in summer and the biomass of small-sized phytoplankton
by means of their feeding activity and excretion of growth-limiting nutrients (Lindén
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& Kuosa, 2004). The bioturbation activity of Mysis relicta can oxygenize the sediment
surface by breaking the diffusive boundary layer; this improves benthic oxygen conditions and promotes colonization of oxygen-poor bottoms by benthic animals (Lindström
& Sandberg-Kilpi, 2008).
Impact of bioinvaders. – Among the few recently published examples for ecological
benefits of non-indigenous species, the invasive mysid Limnomysis benedeni may contribute to higher secondary production and species diversity by its role in leaf litter decomposition in fresh waters (Aßmann et al., 2009). Based on the biosynthesis of polyunsaturated fatty acids by this mysid, Fink (2013) concluded a potential upgrading of the
aquatic food web for native predator species in a recently invaded gravel pit lake, temporarily connected to the Rhine River, Germany.
A major paradigm change in aquatic ecology took place with culminating evidence of
adverse impacts from the anthropogenic expansion of non-indigenous organisms, including mysids: The introduction of Mysis relicta in Norwegian lakes caused decreased
zooplankton density, particularly of cladocerans, and reduced growth of certain fish (Langeland, 1981; Koksvik et al., 1991; Langeland et al., 1991). Daphniids were diminished
in a storage reservoir in the Netherlands due to the invasion of Hemimysis anomala (cf.
Ketelaars et al., 1999). The ecosystems in lakes and coastal lagoons were significantly
altered by deliberate as well as non-deliberate introductions of invertebrates, including
mysids (Lasenby et al., 1986; Olenin & Leppäkoski, 1999; Ojaveer et al., 2002; Bernauer
& Jansen, 2006; Walsh et al., 2012). Biomagnification of toxicants (PCB, Hg) may be enhanced by insertion of an additional trophic level into food webs (Rasmussen et al., 1990;
Wittmann, 2005; Southward Hogan et al., 2007; Wittmann et al., 2010).
As an important component of prevention projects, Ricciardi & Rasmussen (1998)
underlined the necessity of identification and risk assessment of potential biological
invaders. Accordingly, Ricciardi et al. (2012) called for developing predictive models on
the ecological impact of Hemimysis anomala, which is considered a major hazard to the
zooplankton communities of the Laurentian Great Lakes. Ovčarenko et al. (2006) tested
the tolerance of Paramysis lacustris and Limnomysis benedeni to sudden salinity changes
and concluded that a salinity of S 30 could be used as an appropriate biocide in ballast
water treatment to prevent potential transfer of Ponto-Caspian mysids.
Importance in fisheries
Role as food organisms. – In marine to freshwater environments, numerous Lophogastrida and Mysida are found in the stomachs of many species of decapods (Lagardère, 1972,
1977a, b; Siegfried, 1982; Cartes & Abello, 1992; Cartes, 1993a-c) and fish (Sorbe, 1981;
Mauchline, 1982; Astthorsson, 1984; Mauchline & Gordon, 1984a, b; Thiel, 1996; Dürr &
González, 2002; Wittmann et al., 2004; Specziár, 2005; Specziár & Rezsu, 2009; Carrasco
et al., 2012). In certain cases they may play an important role in predator diets. As a striking
example, the mysid Neomysis awatschensis provides 88% of the winter-spring food mass
for Saffron cod in a brackish pool in Kamchatka (Danilin et al., 2012). Abundance of
the mysid Orientomysis mitsukurii shows significant effects on the growth of juvenile
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Japanese flounder Paralichthys olivaceus in the wild (Tomiyama et al., 2013). The mysid
Limnomysis benedeni may be important for fish nutrition because it can biosynthesize
essential polyunsaturated fatty acids from dietary precursors (Fink, 2013). Mysidaceans
are also important food organisms for marine birds, seals, and whales (Feyrer & Duffus,
2011). Upon mass occurrence near the mouth of the Danube River in coastal waters of the
Black Sea, the mysid Mesopodopsis slabberi was formerly used by the local population to
feed domestic animals (Gomoiu, 1978). Considerable amounts of certain marine mysids,
such as Neomysis, Schistomysis, and Praunus, are sold as frozen food for aquarium fish.
In India, Malaysia, and Japan, mysids are used as food for cultured fish, for water birds
in small farms, for pigs, as well as for human nutrition; in this last respect, an important
role is played by the dense populations of Nanomysis in the Java lagoons (Schuster, 1952;
Nouvel, 1957). On certain coasts, mysids are used as a kind of roe. Artisanal fishermen
in Java collect Gastrosaccus yuyu and cook it into a fried rice-flour crisp biscuit, known
locally as “peyek” (Bamber & Morton, 2012). Archaeomysis vulgaris is used in Japan as
dried food called “Ami” and as bait for fish (Matsudaira et al., 1952). Neomysis intermedia
and Neomysis japonica are used in that country for “tsuku-dani”, a popular food boiled in
soy sauce (Murano, 1999b).
Mysids in fisheries management. – Several species of Mysinae (Mysida: Mysidae)
were successfully implanted (“acclimatized”) into impoundment reservoirs and various
other artificial and natural water bodies of eastern and northern Europe, North America,
northern Asia (Lake Aral), and Japan in order to enrich the food basis for commercially
important fish (Zhuravel, 1950, 1969; Karpevich & Bokova, 1963; Murano, 1963, 1966;
Sparron et al., 1964; Gasiunas, 1965, 1968; Linn & Frantz, 1965; Dediu, 1966; Daribaev,
1967; Stringer, 1967; Tjutenkov et al., 1967; Sergeeva & Ckhonelidze, 1968; Gosho,
1975; Fürst, 1981; Langeland, 1981; Bowles et al., 1991; Arbačiauskas, 2002; Aladin et
al., 2003, 2004; Arbačiauskas et al., 2010). The appearance of implanted species in the
stomachs of many species of fish was for several decades emphasized as a confirmation
that the intentional introductions were benefitting fisheries. However, a retrospective
evaluation by Arbačiauskas et al. (2010) did not support a significant enhancement
of fish production after species introductions in Lithuanian lakes. Fürst et al. (1984)
recommended introducing Mysis relicta into Swedish lakes as a measure to reduce
parasitism by tapeworms on benthic char and whitefish. Up to the 1980s there was also
the expectation that the detrimental effects of constructing impoundment reservoirs on
aquatic food chains and biodiversity could be partially compensated by introducing nonindigenous species (Fürst, 1981).
Very soon, however, the expectations of generally positive effects of species introductions turned out to have been unrealistic. A major paradigm change in fisheries management took place in the 1980/90s. The accumulated data pointed to unexpected effects of
deliberately introducing fish food organisms on fish growth, and more generally at the
ecosystem level (see above, ‘Impact of bioinvaders’).
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PHYLOGENY AND BIOGEOGRAPHY
Fossil record
Macrofossils. – The earliest fossil records of mysidaceans (or closely related taxa) are
preserved as moulds in marine sedimentary rock from the Carboniferous to Jurassic. Most
Palaeozoic fossils belong to the extinct Carboniferous to Permian Pygocephalomorpha (a
species-rich order with five families), which were mostly listed as Mysidacea (compilation
in Tattersall & Tattersall, 1951; Taylor et al., 2001), but also as a separate order within
the Eumalacostraca in general (Schram, 1984). Schram (1986) based a separate family,
the Peachocarididae (definition given below, ‘Classification’), on Peachocaris strongi and
Peachocaris acanthouraea from the Carboniferous of North America, and assigned his
new family to the Lophogastrida.
Among Mesozoic fossils, true Lophogastrida with striking similarity to extant forms
were Lophogaster voultensis (family Lophogastridae) and Eucopia precursor (Eucopiidae) from the Middle Jurassic of France (Secretan & Riou, 1986). The assignment of
the Triassic genus Schimperella to the Eucopiidae also appears to be well founded, namely
Schimperella beneckei and Schimperella kessleri from deposits of France (Bill, 1914), and
Schimperella acanthocercus from Guizhou, China (Taylor et al., 2001). The previously
supposed lophogastrids Dollocaris ingens and Kilianicaris lerichei from the Upper Jurassic of France are now identified as Thylacocephala (Secretan, 1985). Among Mysida, clear
records are given for the Middle Jurassic Siriella antiqua and Siriella carinata (cf. Secretan & Riou, 1986). According to Schram (1986), Elder unguiculata and Francocaris
grimmi from the Jurassic of Bavaria are too poorly known for a reliable assignment to the
Mysida.
In contrast to microfossils, Tertiary macrofossils are almost unknown. The family
status as Mysidae appears clear, but not so the generic status of Oligocene fossils of
Mysidopsis oligocenicus, due to a suboptimal state of preservation (De Angeli & Rossi,
2006).
Microfossils. – In most living Mysida, hard mineralized parts predisposed for fossilization are represented mainly by fluorite or carbonate (vaterite) statoliths. So far, fluorite
statoliths were recorded not as fossils but only as subfossil remains from North American
seashores (Enbysk & Linger, 1966). Voicu (1974, 1981) first identified calcareous (calcite)
microfossils (previously considered foraminiferans or calcareous algae) from Miocene deposits of the Paratethys as representing mysid statoliths (fig. 54.27C). At that time the
Paratethys was a large brackish basin extending across Eurasia from the Vienna Basin to
Lake Aral. Likewise, statoliths discovered by Fuchs (1979) in the Vienna Basin were assigned to the Recent genus Paramysis, but later transferred by Maissuradze & Popescu
(1987) to the fossil (Miocene) genus Sarmysis. The basic morphology of these microfossils resembles that of Recent calcareous statoliths. Common peculiar features are the
arch of pores enabling establishment of a ‘statolith formula’ (Voicu, 1974) and the hilum
(Wittmann et al., 1993). The discovery of vaterite (fig. 54.27F; a hexagonal metastable
polymorph of crystalline calcium carbonate) as a normal mineral component of extant
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calcareous statoliths (Ariani et al., 1981, 1983) revealed that the most stable crystal phase
of calcite (fig. 54.27G) present in the fossil material is of secondary nature, namely derived
from phase transformation of the metastable vaterite to the stable calcite (for an overview
of ‘mysid statolithology’ see Ariani, 2004).
No fossil record is known for the Stygiomysida, which have no statoliths. Living
specimens are not completely devoid of mineral structures, as Spelaeomysis longipes
shows spherulite calcareous bodies for calcium storage in caeca of the midgut (Nath,
1972).
Phylogeny
Position within the Malacostraca. – Due to striking morphological coincidence (see
above, ‘Outline of the orders’), Boas (1883) accommodated the Lophogastrida and Mysida
as separate suborders within the order Mysidacea, distinct from the Euphausiacea. This
system remained widely accepted until the early 2000s, even though Siewing (1953),
Watling (1983), Schram (1984), Dahl (1992), Martin & Davis (2001), Kobusch (1999), and
others already had concluded from phylogenetic reconstructions based on morphological
data on Recent and fossil taxa that the Mysida and Lophogastrida are to be placed
separately either within, or outside the Peracarida, respectively. Watling (1983, 1999)
discarded the Peracarida and placed the two orders separately within the Eucarida. Schram
(1984) placed the Lophogastrida within the Peracarida, but the Mysida more distantly
as a sister group of the Peracarida. Based on foregut morphology, Kobusch (1999)
argued for a paraphyly, De Jong-Moreau & J.-P. Casanova (2001) for a monophyly
of the Mysidacea within the Peracarida. A potential monophyly of the Lophogastrida
and Mysida as most basal sister taxa within the Peracarida was also supported by the
parsimonious analysis of 92 morphological characters by Poore (2005).
Based on the structure of the arterial system, particularly the descending artery, Mayrat
et al. (2006) argued against the validity of the Peracarida and proposed a modified revival
of the Podophthalmata, i.e., Malacostraca with stalked eyes and at least a caridoid facies,
extended by the Cumacea. Wirkner & Richter (2007) acknowledged the homology of the
descending artery and a ventral vessel, but emphasized these characters as part of the
plesiomorphic caridoid facies, and thus not useful for uniting taxa into more encompassing
groups. From distinct ostia patterns of the heart and other characters of the circulatory
system, Wirkner & Richter (2007, 2010) and Wirkner (2009) supported the arguments
brought forward by De Jong-Moreau & J.-P. Casanova (2001) for the unity of the
Mysidacea within the Peracarida.
Jenner et al. (2009) performed, among other methods, a parsimony analysis based on
177 morphological characters. This yielded a closer relationship of the Lophogastrida and
Mysida, with both taxa together forming a sister group of the remaining Peracarida. This
is in line with the classical comparative morphology of these taxa, but may also reflect the
persistence of shared plesiomorphic characters in the two (sub)orders.
Jarman et al. (2000) concluded from 28S rDNA data in favour of a polyphyly of
the Mysidacea, with the Mysida closer to the Euphausiacea, and rather distant from the
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Lophogastrida. Martin & Davis (2001) critically evaluated the morphological and genetic
literature available at that time and concluded that the Lophogastrida and Mysida are to
be installed as separate orders, but both within Peracarida. Based on 18S rDNA phylogenetic analysis, Spears et al. (2005) obtained the Lophogastrida as part of a monophyletic
Peracarida clade, whereas the Mysida were allied with some uncertainty to the Stomatopoda, Syncarida, and Eucarida — in any case at great distance from the Lophogastrida.
Similarly, based on 18S and 28S rDNA sequences, in the analysis of Babbitt & Patel
(2005) the Mysida emerged close to the Euphausiacea and Anaspidacea (Syncarida), but
distant from the Peracarida (Lophogastrida not examined). Meland & Willassen (2007)
added a great number of taxa to the dataset of Spears et al. (2005) and concluded to
a disunity of the Mysidacea. In that scheme, the Mysida form a monophyletic group
with low resolution allied to the Euphausiacea and Stomatopoda (unlike Spears et al.,
2005, this clade not including Syncarida and Decapoda). The Lophogastrida and Stygiomysida, in contrast, are located at distant positions from each other within the Peracarida, with the Stygiomysida therein consistently close to the Mictacea. Jenner et al.
(2009) compared different methods of phylogenetic analysis based on four nuclear ribosomal and mitochondrial loci, a morphological dataset, and combinations of these. From
the various methods and their variants — supporting strikingly different trees — they
concluded “that existing molecular and morphological evidence is unable to resolve a
well-supported eumalacostracan phylogeny”. Wills et al. (2009) extended the study of
Jenner et al. (2009) with palaeontological data and obtained very poor coincidence between morphological and stratigraphic signals. A major obstacle to robust phylogenetic
reconstruction can be an early initial radiation. In fact, this is indicated by the fossil
record, insofar as the Eumalacostraca might have appeared in the Devonian, and their
major branches, including the Lophogastrida, were already well formed in the Carboniferous.
Evolution within the Mysida and Lophogastrida. – The uncanny similarity of certain
Jurassic Lophogastrida and Mysida with Recent genera (see above, ‘Fossil record’) also
points to a comparatively early radiation, in this case within these orders. Unlike most
large crustacean orders, only few genetic analyses are available to highlight the relationships within the mysidacean orders discussed here. Based on foregut morphology and 16S
mitochondrial rRNA sequences, J.-P. Casanova et al. (1998) showed that Eucopiidae are
well defined and derived from common ancestors with the Gnathophausiidae (quoted as
Lophogastridae). Based solely on foregut morphology, De Jong-Moreau & J.-P. Casanova
(2001) proposed a basal state of Gnathophausia versus Lophogaster and Eucopia. In contrast, a cladogram by Meland & Willassen (2007: fig. 2b), derived from nuclear 18S rDNA
sequences, hints at Eucopiidae and Gnathophausiidae being potential sister groups, with
common roots with/in the Lophogastridae. Nonetheless, additional data are required for
reliable conclusions in this context.
Remerie et al. (2004) presented a parsimonious tree based on 18S rRNA sequence
data of 25 species of Mysidae. This approach supported the monophyly of subfamilies,
morphologically and taxonomically already distinguished by Hansen (1910), namely the
Siriellinae and the Gastrosaccinae, whereas part of the Mysinae (as Mysini-A clade) un-
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Fig. 54.42. Molecular phylogeny of the Mysida estimated from a Bayesian analysis of nuclear
18S rDNA. The tree represents all families and almost all subfamilies, except Petalophthalminae,
acknowledged in this order. For authorities of species names see ‘Appendix’, for genus names see
‘Classification’. [Modified after Meland & Willassen, 2007.]
expectedly appeared as a sister group of the Siriellinae. Based on 67 (sub)species (fig.
54.42), Meland & Willassen (2007) obtained indication of monophyly for additional subfamilies of Hansen (1910), namely the Boreomysinae, Gastrosaccinae, and Mysidellinae,
whereas the Mysinae appeared again as a heterogeneous assemblage but with a different
pattern compared to that obtained by Remerie et al. (2004). Meland & Willassen (2007)
diminished the numbers of poly-/paraphyletic taxa by raising the former Mysinae tribes
Erythropini, Mancomysini (now Palaumysinae), Heteromysini, and Leptomysini to subfamily level. Nonetheless, some problems remained in the now upgraded Erythropinae and
Leptomysinae as a task for future research. Mitochondrial and nuclear DNA sequences of
no less than 77 species of Mysidae, but covering a smaller number of subfamilies compared to Meland & Willassen (2007), were presented by Porter (2005). Her parsimonious
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tree showed more or less similar clades but in some case fixed at different branches. It also
included a greater number of unexpected single taxa into tribes and subfamilies.
Morphological and biomineralogical analysis. – Evidence from the morphology of
extant animals, macrofossils and microfossils, as well as from the biomineralogy of static
bodies (Ariani et al., 1993), enables tracing a possible phylogeny of the static organ.
Among mysidaceans without a distinct static organ, the Lophogastrida are undoubtedly
the most primitive forms, as shown by their fossil record dating back to the Carboniferous
and the Triassic. Most of their recent species show an oceanic life habit. Together with
the family Petalophthalmidae among Mysida, and with the Stygiomysida, they have
conserved ancestral (plesiomorphic) characters of the Peracarida (if considered a natural
group), particularly seven pairs of oostegites, biramous male pleopods, and the absence of
statocysts in the tail fan.
As mentioned above, due to uncanny morphological coincidences, Secretan & Riou
(1986) assigned Middle Jurassic fossils to the Recent Lophogastrida genera Eucopia and
Lophogaster and to the Recent Mysida genus Siriella. They concluded that there was
little morphological change between the Jurassic forms and their extant congenerics. For
the Mysida, however, they were unable to establish the potential presence or absence
of a statocyst in the endopods of the uropods, which is among the most important
autapomorphic features of the family Mysidae within this order. Similarly, the (badly
preserved) body remains of an Oligocene species are strongly reminiscent of Recent
mysids, so they were tentatively ascribed as belonging to the living genus Mysidopsis (De
Angeli & Rossi, 2006).
The comparatively large (with respect to body size) statoliths contained in the statocysts
can shed some light on the evolution within the family Mysidae (Ariani et al., 1993).
As discussed by Schlacher et al. (1992), the subfamilies Boreomysinae (pelagic) and
Rhopalophthalminae (benthopelagic) have conserved certain plesiomorphic features such
as subdivided exopods of uropods and biramous, multi-segmented male pleopods or,
as in Boreomysinae, seven pairs of oostegites. In both subfamilies, the statoliths are
exclusively non-crystalline (organic). In contrast, the remaining subfamilies (Siriellinae,
Gastrosaccinae, Mysinae, Mysidellinae) show mineralized statoliths and are characterized
by two or three pairs of brood lamellae, reduced pleopods in the females, and mostly
modified pleopods in males. The apparent correlation with plesiomorphic characteristics
suggests that organic statoliths may have preceded mineral ones, as also shown by
ontogenetic evidence from the post-moult development of calcareous statoliths (Ariani
et al., 1982). In contrast to carbonate statoliths, fluorite statoliths are found in most recent
species, but are still unknown in the fossil record. The fluorite-bearing species constitute
the bulk of the extant, benthopelagic to benthic forms inhabiting the coastal and littoral
zones of all oceans. The late appearance of carbonate statoliths as fossil remains (Lower
Miocene according to Voicu, 1981) suggests a post-Cretaceous origin of at least some
genera in the subfamily Mysinae.
Both the scarcity of fossil mysid statoliths outside Paratethyan sediments and biogeographical considerations suggest that carbonate statoliths developed in fresh to brackish
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waters of the Ponto-Caspian region during the Miocene. Selective pressure may have been
at work here, inducing precipitation of a mineral with lower specific gravity than fluorite,
and with a lower demand for fluorine, often poorly available in fresh water (Ariani et al.,
1983). Thus, the precipitation of calcium carbonate as the crystal phase of vaterite is found
in species of Diamysis, Katamysis, Limnomysis, Schistomysis, and particularly Paramysis,
most of which live or have their relatives in the Ponto-Caspian region. Nonetheless, mysids
with vaterite statoliths belonging to the genus Antromysis as well as to certain recently
discovered taxa (K. J. Wittmann, unpublished) live in the Caribbean-Amazonian region,
where an analogous evolutionary process may have occurred.
Biogeography
Historical biogeography. – The problematic distinction between the models of ecological biogeography and those of historical biogeography (Parenti & Ebach, 2009) is
exemplified by the distribution patterns of certain taxa of ‘Mysidacea’. For example, the
distribution of the subterranean genus Stygiomysis (family Stygiomysidae) is restricted to
the Mediterranean and the Caribbean plus surrounding areas, thus well marking the western to central range of the Tethys Sea (Ruffo, 1957; Pesce, 1985; Pesce & Iliffe, 2002).
During the Mesozoic this sea extended from the predecessor of the Caribbean eastward to
what is now the Indian Ocean. Only one additional genus in this order, namely Spelaeomysis (family Lepidomysidae), shows a more circumtropical distribution, but is missing in
the central and western Pacific. The 16 known species of Stygiomysida are characterized
by mostly separate eyestalks (fused in Spelaeomysis longipes) with only few ommatidia or
no visual elements at all. Most species live in fresh water to (mixo)euhaline subterranean
waters, with only Spelaeomysis cardisomae inhabiting small pools at the bottom of crab
burrows (Bowman, 1973), and Spelaeomysis cochinensis inhabiting prawn culture fields
(Panampunnayil & Viswakumar, 1991). The species of Spelaeomysis typically prefer dark
to dimly lit environments; only Spelaeomysis cochinensis is fully exposed to daylight.
Remarkably, Spelaeomysis bottazzii from a brackish well in Apulia (south-eastern Italy)
dwells around the margins of the photic zone for feeding, but seeks shelter in the deep
groundwater during the very long incubation of the young (Ariani & Wittmann, 2010).
Among Mysida from temperate regions, the mainly freshwater to brackish genus
Paramysis offers a good example for a centre of origin (Parenti & Ebach, 2009) as
hypothesized according to classical historical biogeography. This is the Ponto-Caspian
region (a successor of the Paratethys) where 15 out of 23 species live today. The few
remaining species, some having a marine habit, are considered to be of the same origin
from both geographical and ecological points of view. This is also supported by genetic
data of Audzijonyte et al. (2008a). In fact, with only one exception, i.e., the fluorite-bearing
Paramysis arenosa, they share with the Ponto-Caspian species the carbonate (vaterite)
nature of their statoliths (Wittmann & Ariani, 2011). Similarly, all Mediterranean species
of Diamysis have vaterite statoliths (Ariani et al., 1981; Wittmann & Ariani, 1998, 2012a,
b; Ariani & Wittmann, 2000, 2002), unlike the great majority of Mediterranean mysids
with fluorite statoliths. In light of the post-Miocene geo-historical events (Hsü et al.,
1977; Hsü, 1978) the Diamysis species also appear to have a Paratethyan origin; in
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contrast, most other Mediterranean mysids (like marine animals of this region in general)
are undoubtedly of Atlantic origin.
So far there is no clear evidence that Red Sea mysidaceans contributed to the Mediterranean fauna prior to the opening of the Suez Canal. The lophogastrid Lophogaster affinis,
first described from the Red Sea by Colosi (1930), was until just recently cited in faunal
lists for the Mediterranean (Nikoforos, 2002; San Vicente, 2010a), but the Mediterranean
populations actually belong to Lophogaster subglaber, known only from the East Atlantic
and Mediterranean (Wittmann & Riera, 2012). Conversely, previous erroneous reports of
the East-Atlantic-Mediterranean endemic Lophogaster typicus from the Red Sea (Băcescu,
1985) and Indian Ocean (Pillai, 1973) have been attributed (Wittmann et al., 2004) to the
Red Sea endemic Lophogaster erythraeus.
Many populations from cold-temperate to Subarctic freshwater lakes of the Northern
Hemisphere are considered glacial relicts and were previously lumped together as Mysis
relicta (cf. Thienemann, 1925, 1928a, b; Banner, 1948; Holmquist, 1959, 1962). Based
on molecular and morphological data, Audzijonyte & Väinölä (2005, 2006) split Mysis
relicta into four species, and demonstrated that the relict populations belong to Mysis
relicta and Mysis salemaai in northern Europe, to Mysis diluviana in North America. Four
additional species of this genus described by G. O. Sars (1895, 1907) are steno-endemic of
the Caspian Sea. Their ancestors may have invaded this lake from the north, along drainage
systems redirected to the south by glacier barrages in the Pleistocene (Holmquist, 1959).
Ecological biogeography. – The Lophogastrida appear to be generally stenoecious,
at least when compared with the Mysida. Unlike the remaining two mysidacean orders,
the Lophogastrida are exclusively marine. In addition, they are more stenothermic as
indicated by their absence in the Arctic Ocean and by modest species numbers in Antarctic
and Subantarctic waters (Petryashov, 2007, 2009; San Vicente, 2010b), even though most
are deep-water species that are less exposed to temperature variations. Compared to the
mainly bathypelagic and in part panoceanic Gnathophausiidae and Eucopiidae, the more
species-rich Lophogastridae show a more (near-)coastal, benthopelagic distribution, and a
somewhat higher degree of endemism. According to Hargreaves (1989), the large-scale
horizontal distribution of four bathypelagic species of Gnathophausiidae in the eastern
Atlantic is correlated with hydrographical boundaries defined by temperature and oxygen
content.
The Mysida range from tropical to Arctic zones. The numbers of both benthic and benthopelagic species exceed the pelagic ones. The few panoceanic species show a mostly circumtropical distribution, as exemplified by the epipelagic Anchialina typica (Gastrosaccinae) and Siriella thompsonii (Siriellinae). Most pelagic forms are mesopelagic representatives of the Erythropinae. This subfamily also contains bathypelagic and archibenthic
species, mostly belonging to the species-rich genus Pseudomma. Adaptations to deepwater environments are evident in the long thoracic endopods of many Pseudomma spp.
and in the fused eyestalks without ommatidia in all of them (Meland, 2004). Most mysids
are strictly marine, nonetheless about 5% live at least partly in freshwater environments
(S = 0-0.5). Most freshwater species belong to the subfamily Mysinae. According to
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Porter et al. (2008), the “inland” Mysida are mainly euryhaline estuarine species, autochthonous Ponto-Caspian endemics, or glacial relicts.
Areal biogeography. – Petryashov (2005, 2007, 2009) provided extensive information
on areal biogeography and bathymetric distribution of the Lophogastrida in the Arctic,
North Atlantic, North Pacific, and the (Sub-)Antarctic. Several bathypelagic species have
a panoceanic distribution (Brandt et al., 2012), but all of them are missing in the Arctic
Ocean (e.g., Eucopia australis, Gnathophausia zoea, Gnathophausia gigas) and most
of them also in the Southern Ocean (e.g., Eucopia grimaldii, Eucopia sculpticauda,
Chalaraspidum alatum) (Brandt et al., 1998; Petryashov, 2007, 2009; Wittmann & Riera,
2012). Species richness in the Indo-Pacific realms is generally well above that in the
Atlantic, particularly regarding Lophogaster and Paralophogaster. A few examples for
regional vicariance exist, such as the NE-Atlantic-Mediterranean Lophogaster typicus
versus the West Atlantic Lophogaster longirostris.
All species-rich subfamilies of the Mysidae (Mysida) are found around the globe, again
with some exceptions for the Arctic Ocean. However, the frequency of congeneric species
in the Indo-Pacific and the Atlantic realms may differ considerably. For example, besides
the cosmopolitan Siriella thompsonii, 48 species of Siriella are reported from the IndoPacific, and only 13 from the Atlantic (Murano & Fukuoka, 2008). From distributional and
rDNA-based molecular clock data, Meland & Willassen (2004) explained the differences
between ancestral Atlantic and Pacific lineages in the genus Pseudomma by the presence of
this genus in the Tethys Sea already in the Oligocene, followed by subsequent allopatric
divergence due to isolation of the two oceans in the Miocene. Petryashov (2005, 2007,
2009) provided ample data on the areal distribution of mysidaceans in temperate to
Arctic zones, Daneliya & Petryashov (2011) and Daneliya et al. (2012) for mysids of the
Ponto-Caspian and additional Eurasian waters. Using similarity indices based on species
presence, they delineated biogeographical subdivisions for the Arctic, North Atlantic,
Ponto-Caspian, northern Pacific, Subantarctic, and Antarctic. Notably, Petryashov (2007)
distinguished a Notantarctic realm for the pelagic species of Lophogastrida plus Mysida
versus separate Antarctic and Notal realms for the more numerous benthopelagic species
of Mysida (fig. 54.43). In both cases the realms were further subdivided into provinces and
regions.
The Arctic and the Antarctic mysid faunas differ greatly, although a bipolar distribution pattern was reported for three deep-water species (Petryashov, 2007). The warmtemperate to tropical faunas of benthopelagic and benthic mysids show great differences
at the species level between the east and west coasts of both the Atlantic and Pacific
oceans, less strongly also of the Indian Ocean. Several benthopelagic and benthic genera (e.g., Acanthomysis and Heteromysis) are found around the globe, but most show endemism at all levels: from oceans (Indomysis, Kainommatomysis), small sea basins (Calyptomma), down to certain submarine caves (Bermudamysis) or even a single freshwater
cave (Troglomysis).
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Fig. 54.43. Biogeographical division of pelagic (A) and benthopelagic (B) mysidacean
(Lophogastrida plus Mysida) faunas in the Antarctic and Subantarctic. A, Notantarctic realm (1-3)
comprises Circumantarctic (1) and Notal (2-3) provinces, including Patagonian region (3); B,
Antarctic realm (4-7) comprises West Antarctic (4) and East Antarctic (5) provinces, the latter includes the Weddell Sea region (6) and Ross Sea region (7); Notal realm (8-11) comprises South
Chilean (8), Patagonian (9, 10), and Kerguelen (11) provinces; South Georgia region (10) pertains
to the Patagonian province (9, 10). Dashed lines delimit provinces, dotted (almost continuous) lines
regions within provinces. [Modified after Petryashov, 2007, using his terminology.]
Anthropogenic range extension. – Recent, sometimes ample, enlargements of the previously known distribution range of certain species of the subfamily Mysinae are mainly
due to anthropogenic dispersal mechanisms. As already discussed above (‘Importance
for fisheries’), several species were intentionally introduced into fresh waters of Europe,
northern Asia, and North America in order to enrich the food basis for commercially important fish. The freshwater mysids involved were species of Neomysis implanted into
lakes of Japan, glacial relict species of Mysis into waters of northern Europe and North
America, and to a major extent the Ponto-Caspian endemics Paramysis, Limnomysis, and
Hemimysis into waters ranging from central Europe to eastern Asia (Aral Sea). From the
sites of introduction they often spread elsewhere on their own means or as a consequence of
human activity. Some older authors emphasized potential benefits of species introductions
for biodiversity: introductions, including those of mysids, may increase species numbers
and favour recovery from the losses caused by impoundment of water bodies (Fürst, 1981)
or from the heavy natural losses at the last glaciation (Leppäkoski, 1984). Today, the prevailing concern is that native species will be crowded out by introduced ones. Scenarios
presented by Sala et al. (2000) point to biotic exchange as the greatest threat to freshwater biodiversity for the 21st century.
Non-intentional introductions in freshwater bodies were mainly related to fish stocking,
aquaculture, aquaristics, and navigation; the latter involved transport in ballast water, bilge
water, and cooling water filters (Gollasch, 1996; Reinhold & Tittizer, 1998; Wittmann et
al., 1999; Minchin & Rosenthal, 2002; Grigorovich et al., 2003; Nehring, 2005; Ovčarenko
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et al., 2006; Habermehl, 2008; Wittmann & Ariani, 2009; Borza et al., 2011; Arbačiauskas
et al., 2011, 2012). The most important factor for transcontinental dispersion appears to
be the connection of previously separate drainage systems by newly constructed waterways
(fig. 54.44; Tittizer et al., 2000; Leppäkoski et al., 2002; Wittmann, 2007; Wittmann &
Ariani, 2009). The importance of connected waterways for the dispersion of PontoCaspian invertebrates across continental Europe is underlined by the popularized term
‘invasion highways’ (Bij de Vaate et al., 2002; Slynko et al., 2002; Ketelaars, 2004;
Pienimäki & Leppäkoski, 2004; Pöckl et al., 2011).
A stupendous case is that of Limnomysis benedeni (fig. 54.44A), which went up the
Danube River from the Black Sea (Wittmann, 1995, 2007) in at least three independent
waves (Audzijonyte et al., 2009). From here it colonized waters in vast areas of continental
Europe; remarkably it reached the Mediterranean coast by dispersing along rivers and
artificial waterways of France (Wittmann & Ariani, 2000, 2009). Within less than two
decades the Ponto-Caspian freshwater to brackish species Hemimysis anomala (fig.
54.44B) spread mainly along waterways to most of continental Europe, England, Ireland,
and even to the North American Great Lakes (Geissen, 1997; Ricciardi & Rasmussen,
1998; Schleuter et al., 1998; Wittmann & Ariani, 2000; Holdich et al., 2006; Ricciardi,
2007; Audzijonyte et al., 2008b; Minchin & Holmes, 2008; Stubbington et al., 2008;
Borza et al., 2011; Borza & Boda, 2013). The essentially brackish-water species Diamysis
lagunaris reached the Atlantic coasts of Spain and Portugal, possibly by anthropogenic
transfer from Mediterranean lagoons (Cunha et al., 2000), although an indigenous status
of the Atlantic populations is not excluded (Wittmann & Ariani, 2012a).
The Mysida also contributed to the world-wide anthropogenic dispersal of nonindigenous marine invertebrates. This is commonly attributed to transport in ballast water
(Carlton, 1985; Carlton & Geller, 1993), whereas other dispersal mechanisms such as
escape from aquaria, aquaculture, and trade with living aquatic plants or animals appear
unlikely but cannot be excluded for mysids. Similar to the findings in fresh water, most
currently known marine cases pertain to the subfamily Mysinae. Probably ballast water
mediated, transoceanic transfers of Mysinae are exemplified by Praunus flexuosus from
Europe to the U.S. east coast, Neomysis americana from the U.S. east coast to Argentina
and Europe, Neomysis japonica from Japan to Australia, and Acanthomysis aspera from
Japan to the U.S. west coast (Wigley, 1963; Hoffmeyer, 1990; Carlton & Geller, 1993;
Ruiz et al., 2000; Wittmann et al., 2012).
In contrast to fish, decapods, opisthobranchs, and numerous other invertebrates (Ariani
& Serra, 1969; Por, 1978; Dulčić et al., 2004; Yokes & Rudman, 2004; Koukouras et al.,
2010), there is few evidence for a ‘Lessepsian migration’ of Lophogastrida and Mysida
from the Red Sea via the Suez Canal to the Mediterranean or vice versa. The mysid
Kainommatomysis foxi is probably endemic to the Red Sea (Băcescu, 1973c; Almeida
Prado-Por, 1980) but is also found at three stations along the Suez Canal (Por & Ferber,
1972), whereby the northern-most station is the type locality at the Mediterranean coast
(W. M. Tattersall, 1927). No additional records of Kainommatomysis have so far been
reported for the Mediterranean. Pyroleptomysis rubra is endemic to the Mediterranean,
and so far only one specimen was recorded in the Red Sea (Wittmann, 1985).
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Fig. 54.44. Expansion pathways of the mysids Limnomysis benedeni Czerniavsky, 1882 (A), and
Hemimysis anomala G. O. Sars, 1907 (B), from the Ponto-Caspian to western Europe and beyond.
Continuous heavy arrows indicate spread along waterways; dashed heavy arrows indicate deliberate
transplantations. Small dotted lines are artificial navigation canals. Years stand for first records or for
transplantations, respectively. [Original; data updated from Wittmann & Ariani, 2009.]
SYSTEMATICS
Guidelines to classification
Although phylogenetic trees for the three extant orders traditionally assigned to the
Mysidacea are far from being consolidated (see above, ‘Phylogeny’), for the time being
the scheme of Meland & Willassen (2007) is accepted. Already much earlier, Tchindonova
(1981) had concluded from morphological data that (in her terminology) Lophogastrina,
Stygiomysina, Petalophthalmina, and Mysina represent different entities, altogether ranked
by her at suborder level within the Mysidacea. Meland & Willassen (2007) estimated
from genetic data that the Mysidacea actually represent a polyphyletic assemblage of
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three orders, the Lophogastrida, Stygiomysida, and Mysida. Within the order Mysida, they
elevated most former tribes to subfamily level. They did not comment on the classification
by Zimmer (1909), who already a century earlier had defined — with only one exception
— the same families and subfamilies at the same rank. The main difference was that he
placed them within the “suborder Mysidacea” (of course not considering taxa based on
animals discovered after 1909). The recent re-establishment of subfamily ranks liberates
space to re-establish previously neglected tribes, well based by previous authors on
morphological evidence, and to establish eight new tribes within these subfamilies.
Genetic evidence can give supplementary as well as complementary information for
estimation of phylogenies and thus also for classification of morphologically similar
taxa. The trees published by Remerie et al. (2004), Porter (2005), and Meland &
Willassen (2007) (fig. 54.42) for taxa of Mysidae are based on various mitochondrial
and nuclear DNA (RNA) sequences. They show some congruent patterns but also strong
inconsistencies between and especially within subfamilies, possibly due to different taxa
coverage, gene sampling, and statistical treatment. Particularly taxon sampling (numbers
and diversity of taxa) can strongly affect phylogenetic reconstruction (Lecointre et
al., 1993). In conclusion, available genetic data can provide only limited information
in the present context. The limitations are not surprising considering that phylogenetic
reconstruction is hampered by the great age, i.e., early radiation, of mysid morphotypes,
as suggested by the stupefying coincidence between Jurassic fossils (Secretan & Riou,
1986) and living genera.
Based on the above considerations, the classical scheme developed by Hansen (1910),
continued and refined by Illig (1930), Nouvel (1943), W. M. Tattersall (1951), O. S.
Tattersall (1955), Tchindonova (1981), Băcescu & Iliffe (1986), Murano (1986, 1999b),
Nouvel et al. (1999), and many others, is essentially adopted here, with certain higher
taxa ranked according to Zimmer (1909) and Meland & Willassen (2007). Norman
(1892) based the classification within the family Mysidae mainly on the structure of male
pleopods. This character has been in continuous use as the most important diagnostic
tool. This and a number of additional morphological features (including the mineral
composition of static bodies, if present) were used in the present contribution to give
ex novo more precise and consistent diagnoses of the higher taxa. The present approach
was based on physical examination of 73 genera and on published diagnoses available
for 186 currently acknowledged genera (including fossils) pertaining to the three orders
discussed here. Previously forgotten and dismissed taxa above genus level were carefully
reconsidered. The characters of these and proposed new taxa were cross-checked among
each other for consistency within the ranges of uncertainty inherent to phylogenetic
analyses (see above, ‘Phylogeny’). Summing up, the (re)insertion of tribes as an additional
level of classification of the Mysida is certainly at its beginning and could profit from
improvement and consolidation. Such a higher level of taxonomic resolution is intended
to help prompt all branches of biology to take a closer view at the Mysida, for example
regarding morphology, biogeography, biodiversity, ecology, physiology, biomineralogy,
and biochemistry. Finally, the keys given below could be helpful for a short, synthetic look
at the structure of the morphological relationships between the various higher taxa.
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Classification
The first author’s taxonomic database has been in continuous development since 1981.
It was updated by a thorough evaluation of potential synonymies and by crosschecking
with the base of Mees & Meland (2012). This resulted in many modifications of both data
holdings. At the cut-off date 31 December 2012, the total numbers of acknowledged taxa
were 182 genera with 1195 extant species described for the three orders pooled together.
The Lophogastrida contributed with seven genera containing 52 species, the Mysida with
173 genera and 1127 species, and the Stygiomysida with two genera and 16 species. An
additional 13 fossil species were ascribed to a total of four extant and three exclusively
fossil genera (details below). Additions after the cut-off date were one species to the extant
Lophogastrida and three genera and five species (minus one put into synonymy) to the
extant Mysida. The additions and the one withdrawal were integrated in the lists of taxa,
below.
For each order, diagnostic characters are given below down to the tribe level. The
respective taxa inventories are listed down to generic level together with species numbers
in parentheses. The sign † indicates fossil taxa. The families, subfamilies, and tribes are
listed approximately in order of decreasing morphological affinity:
Order LOPHOGASTRIDA Boas, 1883. Carboniferous-Recent (fig. 54.2).
Definition. – Eumalacostraca with well developed, stalked eyes; carapace projects freely over
several posterior thoracomeres; external gills on the coxa of thoracopods 2-7 (8) present at least
in extant taxa, gills covered entirely or in part by the lateral extensions of the branchiostegal
carapace; very large (fig. 54.16A, B) foliaceous thoracic epipod 1 penetrates into carapace cavity;
thoracic exopod 1 reduced to a blade or rod in extant taxa, exopods 2-8 normally well developed,
natatory (exopod 8 missing in Ceratolepis); thoracic endopods vary according to family; females
with 7 pairs of oostegites; at least extant taxa with gonopores on the coxae of thoracopods 6
(females) or 8 (males), the simple slot-like male orifices are not elevated or are on top of a
small elevation, no lobes around orifice and no tubular penes present; all pleopods biramous, well
developed in both sexes, not or weakly modified in males; tail fan strong, endopods of uropods
without statocyst; developmental stages as given below for the Mysida.
Remarks. – Generally large species. Three extant and one fossil family acknowledged. The
four families can be distinguished by the numbers of thoracic endopods specialized as maxillipeds
(gnathopods).
†P EACHOCARIDIDAE Schram, 1986. Carboniferous.
Definition (modified from Schram, 1986). – Integument weakly calcified; thoracic endopod 1 not specialized, all thoracopods alike, well-developed peduncle at the base of the exopods; pleomeres 1-5 with well-developed pleural plates, ultimate pleomere (as far as known)
not divided by a transversal furrow; flat flap-like pleopods; endopod of uropods undivided and
without statocyst.
One fossil genus (type). – †Peachocaris Schram, 1976 (2 species).
L OPHOGASTRIDAE G. O. Sars, 1870. Jurassic-Recent (fig. 54.2B, C).
Definition. – Thoracic endopods 1, 2 developed as maxillipeds; thoracopods 3-8 normal,
usually almost uniform (however, exopod 8 missing in Ceratolepis hamata); all pleomeres
with well-developed pleural plates; ultimate pleomere more or less distinctly divided by a
transversal furrow; both rami of the uropods undivided.
Type genus. – Lophogaster M. Sars, 1856.
Inventory. – Five genera with a total of 34 extant species included: Ceratolepis G. O. Sars,
1884 (1 species), Chalaraspidum Willemoës-Suhm, 1874 (1), Lophogaster (21 extant and
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one fossil species), Paralophogaster M. Sars, 1870 (10), Pseudochalaraspidum Birstein &
Tchindonova, 1962 (1).
G NATHOPHAUSIIDAE Udrescu, 1984 (figs. 54.1A, 54.2A).
Definition. – Integument strongly calcified; rostrum elongate, triquetrous, denticulate;
thoracic exopod 1 very small or missing, exopods 2-8 well developed and multi-segmented;
thoracic endopod 1 developed as maxilliped; thoracopods 2-8 nearly uniform, their endopods
pediform; all pleomeres with well-projecting, bilobate pleural plates; ultimate pleomere more
or less distinctly divided by a transversal furrow; exopod of uropods divided by a subapical
suture, endopod undivided; telson large, dorsally with two long keels, telson constricted near
the base, its apex crescent-shaped.
Only the type genus acknowledged. – Gnathophausia Willemoës-Suhm, 1873 (11 species).
E UCOPIIDAE G. O. Sars, 1885. Triassic-Recent (figs. 54.2D, 54.19A).
Definition. – Integument comparatively soft; antennal scale with short apical segment;
thoracic endopods 1-4 relatively small and specialized as maxillipeds (gnathopods), endopods
2-4 short but strong and subchelate (fig. 54.19A, B), endopods 5-7 very long, thin and also
subchelate, only endopod 8 with normal, pediform structure; pleomeres without projecting
pleural plates; exopod of uropods divided by a subapical suture, endopod undivided; telson
without apical cleft.
Type genus. – Eucopia Dana, 1852 (8 extant and one fossil species). No additional recent
genera known.
One fossil genus. – †Schimperella Bill, 1914 (3 species).
Order STYGIOMYSIDA Tchindonova, 1981 (fig. 54.3).
Definition. – Eumalacostraca with eyestalks generally separate (fused only in Spelaeomysis
longipes), ranging from vestigial to well developed and moveable, cornea missing or reduced to
a small number of ommatidia; sizes of the respiratory carapace and of the foliaceous thoracic
epipod 1 vary according to family; gills absent; first pair of thoracopods with the exopod reduced
to a leaf-like blade, exopods 2-8 well developed, natatory; anterior 3-4 pairs of thoracic endopods
modified as maxillipeds, remaining endopods pediform (among a total of 8 pairs); 4-7 pairs of
oostegites; gonopores on the coxae of thoracopods 6 (females) or 8 (males), male gonopores
flanked by an anterior setose and a posterior bare lobe, no penes present; pleopods biramous,
but somewhat rudimentary in both sexes, sympod and endopod unsegmented, but exopod with a
small number of segments; tail fan strong, sympod of uropod with spinose inner lobe, statocysts
absent; developmental stages as given below for the Mysida.
Remarks. – Two families with one genus each, total of 16 species. Most species stygobiotic
(cavernicolous or phreatobious). No fossils known.
L EPIDOMYSIDAE Clarke, 1961 (figs. 54.1C, 54.3B-D, 54.19C, D).
Definition. – Antennal scale well developed; the large carapace projects freely backward
over several posterior thoracomeres, cervical sulcus absent; comparatively large (fig. 54.17A)
thoracic epipod 1 penetrates into the well-formed carapace cavity; maxillula with palp;
thoracic endopods 1-3 modified as maxillipeds, endopods 4-8 pediform; oostegites on
thoracopods 2-8; pleopods with 3-4 segmented exopod; sympod of uropod with small,
spinose inner lobe, exopod unsegmented or divided by a distinct or indistinct suture, endopod
unsegmented; telson linguiform, its margins with spines and distally also plumose setae.
Type genus. – Lepidomysis Clarke, 1961a (junior synonym of Spelaeomysis).
Only one genus acknowledged. – Spelaeomysis Caroli, 1924 (9 species).
S TYGIOMYSIDAE Caroli, 1937 (figs. 54.1B, 54.3A).
Definition. – Antennal scale vestigial; carapace short, dorsally completely fused with the
anterior thoracomeres — this makes the body appear vermiform; maxillula without palp; only
a small (fig. 54.17B) thoracic epipod 1 penetrates into the small carapace cavity; thoracic
endopods 1-4 modified as maxillipeds, endopods 5-8 pediform; oostegites on thoracopods
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4-7; pleopods with 2-4 segmented exopod; sympod of uropod with large inner lobe with its
apical spines extending beyond the endopod, exopod and endopod unsegmented; telson about
lozenged to subrectangular, terminally with spines.
Only type genus known. – Stygiomysis Caroli, 1937 (7 species).
Order MYSIDA Boas, 1883. Jurassic-Recent (figs. 54.4, 54.5).
Definition. – Eumalacostraca with eyes mostly well developed, stalked, less frequently reduced or modified in various ways; carapace always well developed, projecting freely over several posterior thoracomeres (except in Palaumysis philippinensis), its cavity lined with respiratory
tissue; no gills developed; mostly intermediate-sized (fig. 54.15M), foliaceous thoracic epipod 1
penetrates into carapace cavity; thoracic exopods 1-8 usually well developed, natatory (exopods
1, 2 reduced or missing in certain taxa); thoracic endopods 1, 2 specialized as maxillipeds, endopods 4-7 pediform, endopods 3, 8 pediform or modified; 1-7 pairs of functional oostegites;
gonopores on the coxae of thoracopods 6 (females) or 8 (males), tubular penes present (except in
Rhopalophthalminae), penes with (sub)terminal orifice and one or more terminal lobes; pleopods
2-5 (mostly also 1) reduced to unsegmented plates or rods in females (but biramous in Archaeomysis); partly also reduced in males; 1-2 pairs of pleopods with particular modifications in males
of most taxa; tail fan well-formed, sympod of uropods without endite, statocysts present only
in the family Mysidae; embryonic and two larval stages (nauplioids, postnauplioids) develop in
the brood pouch; all post-marsupial stages free-living, self-sustaining; freshly hatched juveniles
resemble miniature adults but lack secondary sexual characteristics.
Nomenclatorial note. – There is a current trend (e.g., Anderson, 2010) to quote Haworth
(1825) as the author of the Mysida. However, Haworth (1825) established the Mysidae only
at family level. Article 35.1. of the code of nomenclature (ICZN, 1999) applies only up to
superfamily level. Boas (1883) defined the Mysida for the first time by establishing this taxon
at suborder level. His authorship was in continuous use until just recently and, therefore, is
recommended to be applied further.
P ETALOPHTHALMIDAE Czerniavsky, 1882 (figs. 54.4A, 54.5A).
Definition. – Eyes modified in various ways, less frequently normal; maxillula without
palp; thoracopod 1, often also thoracopod 2, without natatory exopod; merus of thoracic endopod 2 with a large lobe-like expansion (= endite); females with seven pairs of oostegites;
tubular penes present; pleomeres without projecting pleural plates; female pleopods uniramous or biramous; male pleopods always biramous, all their exopods and most endopods
multi-segmented; exopods of uropods with or without subterminal suture, endopods not subdivided, without statocyst.
Inventory. – Two subfamilies with a total of 6 genera and 38 species. Most species
bathypelagic and/or archibenthic. No fossils known.
P ETALOPHTHALMINAE Czerniavsky, 1882 (figs. 54.4A, 54.12B).
Definition. – Eyes normal or modified, visual elements present or absent; males with
basally moderately thickened, inner antennular flagellum; mandibular palp long, powerful,
and prehensile; only first thoracopod without exopod; female pleopods uniramous or
biramous; exopods of uropods with subterminal suture.
Type genus. – Petalophthalmus Willemoës-Suhm, 1874.
Inventory. – Three genera with a total of 8 species: Parapetalophthalmus Murano &
Bravo, 1998 (1 species), Petalophthalmus (5), Pseudopetalophthalmus Bravo & Murano,
1997 (2).
H ANSENOMYSINAE new subfamily (figs. 54.5A, 54.12A, 54.25M).
Definition. – Eyes fused in a single plate, mostly without or with few visual elements;
males with modified, strongly thickened, inner antennular flagellum; mandibular palp normal, not prehensile; first and second thoracopods without exopods; pleomeres without projecting pleural plates (but with spiniform extensions in Ceratomysis); female pleopods uniramous, reduced to (1-3)-segmented rods; exopods of uropods with or without (Bacescomysis) subterminal suture.
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Type genus. – Hansenomysis Stebbing, 1893, by present designation.
Inventory. – Three genera with a total of 30 species: Bacescomysis Murano & Krygier,
1985 (7 species), Ceratomysis Faxon, 1893 (5), Hansenomysis (18).
M YSIDAE Haworth, 1825. Jurassic-Recent (figs. 54.4B-M, 54.5B-M).
Definition. – All eight pairs of thoracopods normally with natatory exopod (first pair
reduced to laminae in Mysimenzies); merus of thoracic endopod 2 without large lobe-like
expansion; well-developed tubular penes except in Rhopalophthalmus; endopods of uropods
normally undivided (subdivided in Rhopalophthalmus), always with statocyst. Statoliths nonmineralized (organic) or composed of fluorite (CaF2 ) or calcium carbonate (CaCO3 ), the latter
in the crystal phases of vaterite or calcite in the extant and fossil forms, respectively.
Inventory. – Ten extant subfamilies are acknowledged here according to Meland &
Willassen (2007), except for the nomen nudum ‘Mancomysinae’, which was replaced by
Palaumysinae Wittmann, 2013b. The Mysidae comprise 170 genera with a total of 1093 living
species; six extinct species are assigned to one exclusively fossil plus three Recent genera.
B OREOMYSINAE Holt & Tattersall, 1905 (figs. 54.4B, 54.5B).
Definition. – Smooth outer margin of the antennal scale ending in a non-articulate
spine; penes well developed, tubular; seven pairs of oostegites; thoracopods normal;
pleomeres without projecting pleural plates in both sexes; females with pleopods reduced
to unsegmented rods; male pleopods biramous, endopod 1 undivided, remaining endopods
and all exopods multi-segmented, without apparent modifications except for some elongation of exopods 2, 3; exopod of uropods divided by a proximal, incomplete suture; statocyst
containing a small, non-mineralized statolith; telson with apical cleft.
Type genus. – Boreomysis M. Sars, 1869.
Two genera included. – Birsteiniamysis Tchindonova, 1981 (2 species), Boreomysis
(36).
R HOPALOPHTHALMINAE Hansen, 1910 (figs. 54.4C, 54.5C).
Definition. – Antennal scale well developed, with smooth outer margin ending in
a non-articulate spine; thoracic endopods 1-7 as normal in Mysidae, endopod 8 small
or minute, reduced to 1-3 segments showing distinct sexual dimorphism; three pairs of
oostegites; no penes developed, bilobate male gonopores located on the inner terminal
margin of the strongly enlarged coxae of thoracopod 8; male pleomere 1 with wellprojecting, rounded pleural plates; remaining pleomeres of males and all pleomeres of
females without projecting pleurae; female pleopods reduced to unsegmented, setose rods;
male pleopods biramous, both rami multi-segmented with exception of the unsegmented,
plate-like, first endopod; male pleopod 2 with modified, elongate exopod; both rami of the
uropods subdivided by a transverse suture, exopod setose all around and without spines;
statocyst with almost spherical, non-mineralized statolith; telson entire, linguiform, its
margins distally armed with spines.
Only the type genus known. – Rhopalophthalmus Illig, 1906 (25 species).
S IRIELLINAE Czerniavsky, 1882 (figs. 54.4D, 54.5D, 54.26A).
Definition. – Eyes normal; antennal scale well developed, with smooth outer margin
ending in a non-articulate spine; labrum mostly with long frontal, spiniform process;
thoracic endopods 3-8 with unsegmented or rarely with two-segmented propodus, peculiar
brush of setae around dactylus; penes well developed, tubular; three pairs of oostegites;
pleomeres without projecting pleural plates; female pleopods uniramous, unsegmented,
representing small rods (plates); male pleopods vary according to tribe; endopod of
uropods undivided, exopod with spines on outer margin of the basal segment, short
terminal segment separated by a mostly oblique suture, this segment setose all around;
statocyst with flattened, fluorite statolith; telson linguiform with spines on lateral margins.
Inventory. – Two tribes are distinguished according to the structure of the male
pleopods. They comprise a total of 3 genera with 85 extant plus 2 fossil species.
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Siriellini Czerniavsky, 1882 (figs. 54.4D, 54.5D, 54.26A).
Definition. – Male pleopods biramous, multi-segmented (endopod of the first pair
rudimentary), basal segment of endopods with spirally coiled or curved, less frequently
straight exites (= pseudobranchial lobes); modified setae may be present (or not) on
exopod or endopod or both of any among pleopods 2-4.
Type genus. – Siriella Dana, 1850.
Two genera included. – Hemisiriella Hansen, 1910 (4 species), Siriella (80 extant
plus 2 fossil species).
Metasiriellini Murano, 1986.
Definition. – Male pleopods 1-3, 5 rudimentary, uniramous, and unsegmented as in
females; male pleopod 4 with two multi-segmented rami, basal segment of endopod
with straight, rod-like exite (= pseudobranchial lobe).
Only the type genus known. – Metasiriella Murano, 1986 (1 species).
G ASTROSACCINAE Norman, 1892 (figs. 54.4E, F, 54.5E, F).
Definition. – Eyes normal; antennal scale well developed, smooth outer margin ending
in a non-articulate spine; two pairs of oostegites; first pleomere with pleural plates
normally in females only (in Archaeomysis in both sexes); pleopods of both sexes vary
according to tribe; both rami of the uropods undivided, exopod with spines on outer margin
in most taxa; statocyst with (generally small) fluorite statolith. Telson with spines on lateral
margins, its apical cleft armed with spine-like laminae.
Nomenclatorial note. – The precedence of the family group taxon Pontomysidae Czerniavsky, 1882 (as “Divisio” = tribus), over the junior synonym Gastrosaccinae Norman,
1892, is inverted here according to Article 23.9.1 of the code of nomenclature (ICZN,
1999). The senior synonym was last used by Czerniavsky (1887). The junior synonym has
been in continuous use since Norman (1892), by far exceeding the requirements of Article
23.9.1.2.
Inventory. – Three tribes are distinguished based on to the structure of pleural plates
and pleopods. They comprise a total of 10 genera with 96 species.
Archaeomysini Czerniavsky, 1882.
Definition. – First pleomere (in part also the second) of females with large pleural
plates covering and supporting the marsupium from behind, in part also from the side;
such plates also present in males, but smaller; certain taxa with plates on additional
pleomeres, whereby plate size decreases from pleura 2 to 5; pleopods biramous in both
sexes, exopod of pleopod 3 elongated in males only.
Only the type genus known. – Archaeomysis Czerniavsky, 1882 (6 species).
Gastrosaccini Norman, 1892 (figs. 54.4F, 54.5F).
Definition. – Only first pleomere of females with large pleural plates covering and
supporting the marsupium from behind, in part also from the side, no such plates
in males; female pleopod 1 biramous, pleopods 2-5 uniramous, unsegmented; male
pleopods biramous or reduced in various ways, exopod 3 (exceptionally exopod 4)
particularly long and modified (mostly styliform or with complex structure in certain
genera).
Type genus. – Gastrosaccus Norman, 1868.
Six genera included. – Chlamydopleon Ortmann, 1893 (3 species), Coifmanniella
Heard & Price, 2006 (4), Eurobowmaniella Murano, 1995 (2), Gastrosaccus (24),
Haplostylus Kossmann, 1880 (25), Iiella Băcescu, 1968 (9).
Anchialinini new replacement name (figs. 54.4E, 54.5E).
Formation of the replacement name. – According to article 39 of the code of
nomenclature, a family group name is invalid if based on a junior homonym (ICZN,
1999). The family group name Anchialidae Czerniavsky, 1882, is based on the mysid
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genus Anchialus Krøyer, 1861, a junior homonym of the coleopteran genera Anchialus
Gistel, 1834, and Anchialus Thomson, 1859, and is therefore to be replaced by a family
group name based on the valid replacement name Anchialina Norman & Scott, 1906,
for the former type genus.
Definition. – Only first pleomere of females with small pleural plates covering a
small part of the marsupium, no such plates in males; female pleopods uniramous,
unsegmented; male pleopod 1, in part also 4, 5, rudimentary and resembling those
of females, remaining pleopods biramous, exopod 3 modified in various, sometimes
complex ways.
Revised type genus. – Anchialina Norman & Scott, 1906 (replacement name for
Anchialus Krøyer, 1861), by present designation.
Three genera included. – Anchialina (17 species), Paranchialina Hansen, 1910 (2),
Pseudanchialina Hansen, 1910 (4).
E RYTHROPINAE Hansen, 1910 (figs. 54.4G, 54.5G).
Definition. – The eyes show a great diversity from well-developed to reduced, platelike, according to taxon; antennal scale normally well-developed (rudimentary in Arachnomysis, Caesaromysis, Chunomysis, Gymnerythrops) with mostly smooth outer margin
ending in an articulate or a non-articulate spine; thoracic endopods 3-8 with the carpus
separated from the propodus in most genera by an oblique articulation, less frequently
with transverse articulation; females with 2-3 (4) pairs of oostegites; pleomeres without
projecting pleural plates in both sexes; pleopods 1-5 in females are uniramous and unsegmented, endopod of pleopod 1 in males uniramous, exopod 1 and both rami of pleopods
2-5 vary in males according to tribe, exites of endopods never curved or coiled; both rami
of the uropods undivided; statocyst with fluorite statolith; telson entire or rarely terminally
indented or cleft.
Nomenclatorial note. – The senior synonym Protomysidellinae Czerniavsky, 1882, was
no longer used as a valid taxon after Czerniavsky (1887) and is invalid because of being
not based on an available generic name (Article 11.7.1.1 of ICZN, 1999).
Inventory. – Eight tribes are distinguished according to the structure of eyes, antennular
peduncle, antennal scale, antennal gland, labrum, articulation between carpus and propodus of the posterior thoracic endopods, male pleopods, and telson. Altogether, the eight
tribes comprise 54 genera with a total of 243 species.
Erythropini Hansen, 1910 (fig. 54.5G).
Definition. – Eyes mostly with, or in a few taxa without visual elements, eyestalks
well separated from each other; antennal scale well developed, antennal gland normal
or hypertrophic; labrum normal; thoracic endopods 3-8 with mostly oblique (rarely
transverse) articulation between carpus and propodus; 2-3 pairs of oostegites; endopod
of male pleopod 1 reduced to a single segment, exopod 1 rarely entire but mostly multisegmented, male pleopods 2-5 well developed, biramous; in several genera modified
setae may be present on any of male pleopods 3-5, mostly on endopods; telson entire,
lateral margins generally smooth (never serrate), in some taxa with spines laterally on
terminal portions, in certain taxa with a pair of medio-apical setae.
Type genus. – Erythrops G. O. Sars, 1869.
Thirty-five genera included. – Aberomysis Băcescu & Iliffe, 1986 (1 species),
Amathimysis Brattegard, 1969 (9), Atlanterythrops Nouvel & Lagardère, 1976 (1),
Australerythrops W. M. Tattersall, 1928 (2), Dactylamblyops Holt & Tattersall, 1906
(15), Dactylerythrops Holt & Tattersall, 1905 (5), Echinomysides Murano, 1977 (1),
Echinomysis Illig, 1905 (3), Erythrops (17), Euchaetomera G. O. Sars, 1883 (9),
Euchaetomeropsis W. M. Tattersall, 1909 (2), Gibbamblyops Murano & Krygier,
1985 (1), Gibberythrops Illig, 1930 (4), Heteroerythrops O. S. Tattersall, 1955 (3),
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Holmesiella Ortmann, 1908 (3), Hyperamblyops Birstein & Tchindonova, 1958 (5),
Hypererythrops Holt & Tattersall, 1905 (8), Illigiella Murano, 1981 (1), Indoerythrops
Panampunnayil, 1998 (1), Katerythrops Holt & Tattersall, 1905 (4), Liuimysis Wang,
1998 (1), Longithorax Illig, 1906 (6), Meierythrops Murano, 1981 (2), Metamblyops
W. M. Tattersall, 1907 (3), Meterythrops S. I. Smith, 1879 (7), Nakazawaia Murano,
1981 (2), Nipponerythrops Murano, 1977 (1), Parerythrops G. O. Sars, 1869 (6),
Pleurerythrops Ii, 1964 (5), Pseudamblyops Ii, 1964 (1), Pseuderythrops Coifmann,
1936 (3), Pteromysis Ii, 1964 (1), Shenimysis Wang, 1998 (1), Synerythrops Hansen,
1910 (3), Teraterythrops Ii, 1964 (2).
Remark. – The morphological heterogeneity together with genetic data of Meland &
Willassen (2007) suggest that this tribe is polyphyletic. More data on a greater diversity
of genera are wanted.
Arachnomysini Holt & Tattersall, 1905 (figs. 54.7F, 54.12C).
Revised definition. – Eyes well developed, separate and stalked; carapace anteriorly
without or with series of spines; antennal scale missing or vestigial; labrum normal;
thoracic endopods 3-8 with the carpus separated from the propodus by a transverse or
a slightly oblique articulation; endopod of male pleopod 1 reduced to a single segment,
exopod multi-segmented, male pleopods 2-5 well developed, biramous; marsupium
with two pairs of oostegites; telson subtriangular, without or with small medio-apical
indentation, lateral margins smooth.
Type genus. – Arachnomysis Chun, 1887.
Four genera included. – Arachnomysis (2 species), Caesaromysis Ortmann, 1893
(1), Chunomysis Holt & Tattersall, 1905 (1), Gymnerythrops Hansen, 1910 (3 species,
males unknown).
Inusitatomysini new tribe.
Definition. – Eyes with well-developed cornea on separate eyestalks; antennal
scale well developed, its outer margin proximally smooth, centrally and distally
serrate, ending in a non-articulate spine; antennal gland and labrum normal; posterior
thoracic endopods with some sub-segments of the carpopropodus separated by oblique
articulations from each other; three pairs of well-developed oostegites plus a pair of
vestigial ones on thoracic endopod 5; all pleopods uniramous, represented by endopods
in both sexes, these endopods reduced to unsegmented plates, with the only exception
that endopod 4 is elongate, multi-segmented, and apically furnished with modified setae
in males; uropods setose all around, endopod with one spine on outer margin below
statocyst; telson large, its lateral margins with spines, but not serrate, strong apical cleft
furnished with a pair of plumose setae emerging from its bottom, margins of cleft lined
by spine-like laminae.
Only the type genus known. – Inusitatomysis Ii, 1940 (1 species), by present
designation.
Remarks. – Based on the reduction of most male pleopods, this aberrant genus was
placed by W. M. Tattersall (1951) and Ii (1964) in the Mysini (now Mysinae). In the
present study it is shifted as a separate tribe to the Erythropinae due to the modification
of the endopod — unlike the exopod as in Mysinae — of the fourth male pleopod.
The structure of the antennal scale and the eyes closely resemble those in Erythrops
serratus and Erythrops abyssorum. The reduced oostegite on thoracic endopod 5 is
reminiscent of the small but well-developed brood plate found in the same position in
Thalassomysis.
Thalassomysini Nouvel, 1942b.
Definition. – Eyes with well-developed separate eyestalks, cornea reduced to a
varying extent; antennal scale well developed, setose all around; labrum strongly
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asymmetrical; thoracopods 3-8 with the carpus separated from the propodus by a
transverse articulation; four pairs of oostegites; uropods setose all around, without
spines; telson entire, elongate, its lateral margins with spines, but not serrate.
Only the type genus known. – Thalassomysis W. M. Tattersall, 1939 (2 species,
males unknown).
Remark. – The placement of Thalassomysis is difficult as long as the males remain unknown. W. M. Tattersall (1939) placed it with query in the Erythropini, Nouvel (1942b) into a special subfamily, the Thalassomysinae, Pillai (1965) in the Leptomysini, Murano & Krygier (1985) and Nouvel et al. (1999) back to the Thalassomysinae, and Meland & Willassen (2007) again back to the Erythropinae. Here, it is also
placed in the Erythropinae, but in a separate tribe due its aberrant morphology.
Amblyopsini Tchindonova, 1981 (figs. 54.4G, 54.18D).
Revised definition. – Eyes separate, eyestalks reduced to immotile plates, visual
elements rudimentary or absent; antennal scale well developed, its smooth outer margin
ending in a non-articulate spine, antennal gland mostly hypertrophic; labrum normal;
thoracopods 3-8 with the carpus separated from the propodus by an oblique articulation;
2-3 pairs of oostegites; endopod of male pleopod 1 reduced to a single segment, exopod
multi-segmented, male pleopods 2-5 well developed, biramous; a number of species
shows (sub)apical, modified setae in some of male pleopods 2-4, most frequently on
exopod 4; telson entire, lateral margins smooth (not serrate), only terminally or all
along with spines, two (sub)apical setae present in some species.
Type genus. – Amblyops G. O. Sars, 1872.
Six genera included. – Amblyops (22 species), Amblyopsoides O. S. Tattersall,
1955 (4), Eoamblyops Murano, 2013 (1), Paramblyops Holt & Tattersall, 1905 (8),
Scolamblyops Murano, 1974 (1), Teratamblyops Murano, 2001 (3).
Mysimenziesini Tchindonova, 1981.
Revised definition. – Eyes rudimentary, without visual pigment, the rudimentary
eyestalks resemble horns and are connected by a median bridge; basal segment of
antennular peduncle medio-dorsally with sensory fossette or with setose elevation;
antennal scale well developed, with smooth outer margin ending in a non-articulate
spine; labrum normal; thoracic endopods 3-8 with oblique or transverse articulation
between carpus and propodus; three pairs of oostegites; male pleopod 4 biramous
with both rami multi-segmented, modified setae at tip of endopod 4, remaining male
pleopods uniramous or biramous; telson truncate (in part terminally slightly indented),
its lateral margins distinctly serrate.
Type genus. – Mysimenzies Băcescu, 1971a.
Two genera included. – Marumomysis Murano, 1999a (2 species), Mysimenzies (2).
Remark. – The first detection of males and of additional taxa (Murano, 1999a;
San Vicente, 2007; Fukuoka, 2009) confirmed previous assumptions (Băcescu, 1971a;
Nouvel et al., 1999; Meland & Willassen, 2007) that Mysimenzies is to be placed in the
Erythropinae. The recent findings confirmed the aberrant morphology of these mysids,
leading here to revalidation of the Mysimenziesinae at tribe rank.
Pseudommini new tribe (figs. 54.20C, 54.21J, 54.25P).
Definition. – Both eyes fused to a common plate with anterior, median cleft, visual
elements missing, posterior parts of eyeplate ventrally fused with basal parts of antennulae and antennae; antennal scale well developed, its smooth outer margin ending in
a non-articulate spine, antennal gland hypertrophic; labrum normal; thoracopods 3-8
with the carpus separated from the propodus by an oblique articulation; two pairs of
oostegites; endopod of male pleopod 1 reduced to a single element, exopod 1 multisegmented, male pleopods 2-5 well developed, biramous: modified setae, if present,
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mainly on fourth endopod; telson entire, linguiform to nearly lozenged, its lateral margins entirely smooth or only proximally smooth with spines along terminal portions.
Type genus. – Pseudomma G. O. Sars, 1870, by present designation.
Three genera included. – Neoamblyops Fukuoka, 2009 (1 species), Parapseudomma
Nouvel & Lagardère, 1976 (1), Pseudomma (45). The species Parapseudomma calloplura and Pseudomma oculospinum are included here based on eye morphology (for
different views see Murano, 1974; Meland, 2004; Meland & Willassen, 2007).
Calyptommini W. M. Tattersall, 1909.
Definition. – Both eyes fused to a common lamina without cleft, visual elements
rudimentary or absent; antennal scale well developed, its smooth outer margin ending
in a non-articulate spine; antennal gland hypertrophic; labrum normal; pleopods of both
sexes reduced to unsegmented, rod-like endopods that increase in length caudally, the
ultimate pleopods 4, 5 most elongate in males; telson entire, lateral margins not serrated
but mostly smooth, terminal portions with spines.
Type genus. – Calyptomma W. M. Tattersall, 1909.
Two genera included. – Calyptomma (1 species), Michthyops W. M. Tattersall, 1911
(3).
L EPTOMYSINAE Czerniavsky, 1882 (figs. 54.4H, 54.5H).
Definition. – Eyes mostly normal, a few taxa with modified cornea; antennal scale
setose all around and in most taxa with small terminal segment; thoracic endopods 3-8
with carpopropodus subdivided by transverse articulations into more than two segments;
females with three, rarely two, pairs of oostegites; pleomeres without projecting pleural
plates in both sexes; female pleopods reduced to small, unsegmented endopods; male
pleopod 1 biramous with unsegmented endopod and multi-segmented exopod (exopod
missing in Pyroleptomysis); male pleopods 2-5 biramous, both rami multi-segmented,
exopod of pleopod 4 modified and/or with modified setae; both rami of the uropods
undivided, exopods without spines, setose all around; statocyst with fluorite statolith.
Inventory. – Three tribes are distinguished based on the structure of maxilla, thoracic
endopod 1, and telson. Altogether, they comprise 30 genera with 164 extant plus one fossil
species.
Mysidopsini new tribe (figs. 54.15L, 54.18F, 54.22N).
Definition. – Antennal scale setose all around, mostly with small terminal segment;
exopod of maxilla narrow or absent; first thoracic endopod only (5-6)-segmented, its
ischium fused with the merus; coxa may show a small conical endite, no endites on
basis or the fused merischium (fig. 54.15L versus 54.15M); females with three pairs
of well-formed oostegites (the first one very small); telson mostly entire, or with small
apical indentation, its margins with spines but without setae.
Type genus. – Mysidopsis G. O. Sars, 1864, by present designation.
Five genera included. – Americamysis Price & Stuck, 1994 (6 species), Brasilomysis
Băcescu, 1968 (2), Cubanomysis Băcescu, 1968 (2), Metamysidopsis W. M. Tattersall,
1951 (8), Mysidopsis (48 extant plus one fossil species).
Leptomysini Czerniavsky, 1882 (figs. 54.4H, 54.5H, 54.21N, 54.36E-F, 54.37).
Definition. – Antennal scale setose all around, with small terminal segment; exopod
of maxilla laterally well expanded, endopod normal; first thoracic endopod sevensegmented, i.e., ischium and merus not fused, endites may be present on coxa and
basis, often also on ischium; females with three pairs of well-formed oostegites (fig.
54.19K-H); telson entire or with minute cleft, telson lined by spines along most of its
margins, never by laminae or apical setae (plumose setae may be present on ventral
face but not on margins).
Type genus. – Leptomysis G. O. Sars, 1869.
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Six genera included. – Antichthomysis Fenton, 1991 (1 species), Leptomysis (9),
Megalopsis Panampunnayil, 1987 (1), Paraleptomysis Liu & Wang, 1983 (5), Pyroleptomysis Wittmann, 1985 (2), Notomysis Wittmann, 1986 (1).
Afromysini new tribe (fig. 54.25F).
Definition. – Antennal scale setose all around, without or in most taxa with
small terminal segment; exopod of maxilla laterally well expanded, distal segment of
endopod often terminally widened and with spines or teeth on terminal margin; first
thoracic endopod seven-segmented, i.e., ischium and merus not fused, endites present
on coxa and basis, often also on ischium and merus; females mostly with three pairs
of well-developed oostegites, rarely with only two; telson apically with cleft or less
frequently narrowly truncate, lateral margins lined by spines; apical cleft, if present,
mostly with two plumose setae emerging from or close to its bottom, margins of cleft
smooth or lined by spine-like laminae.
Type genus. – Afromysis Zimmer, 1916, by present designation.
Nineteen genera included. – Afromysis (7 species), Australomysis W. M. Tattersall,
1927 (5), Bathymysis W. M. Tattersall, 1907 (2), Ceratodoxomysis Murano, 2003
(1), Dioptromysis Zimmer, 1915 (5), Doxomysis Hansen, 1912 (17), Hyperiimysis
H. Nouvel, 1966 (1), Iimysis H. Nouvel, 1966 (3), Mysideis G. O. Sars, 1869 (2),
Neobathymysis Bravo & Murano, 1996 (2), Neodoxomysis Murano, 1999 (3), Nouvelia
Băcescu & Vasilescu, 1973 (3), Prionomysis W. M. Tattersall, 1922 (4), Promysis Dana,
1850 (2), Pseudobranchiomysis Carcedo, Fiori & Hoffmeyer, 2013 (1), Pseudomysis
G. O. Sars, 1879 (2), Pseudoxomysis H. Nouvel, 1973 (3), Rostromysis Panampunnayil,
1987 (1), Tenagomysis G. M. Thomson, 1900 (15).
M YSINAE Haworth, 1825 (figs. 54.1E, 54.4J, 54.5J, 54.36A, B).
Definition. – Eyes well developed, eyestalks always separate, only few taxa with modified or reduced cornea; antennal scale variable; thoracic endopods 3-8 with carpopropodus
subdivided by transverse articulations, or exceptionally not divided; females with 2-3 pairs
of oostegites; pleomeres without projecting pleural plates; female pleopods reduced to simple, unsegmented rods; male pleopods 1 and 2 (mostly also 5) rudimentary as in females;
male pleopod 3 biramous and/or reduced to different degrees, male pleopod 4 normally
biramous, with elongate exopod and modified setae; both rami of the uropods undivided,
exopods without spines, setose all around; statocyst with statolith composed of fluorite or
less frequently of vaterite (calcite in fossil taxa; cf. above, ‘Microfossils’).
Inventory. – Four tribes are distinguished based on the structure of antennal scale,
oostegites, male pleopods, and telson. Altogether, they comprise 53 extant genera with
297 species plus one fossil genus with 3 species.
Mysini Haworth, 1825 (figs. 54.1E, 54.5J).
Definition. – Antennal scale mostly with short apical segment, scale setose all
around or with (over part of its length) bare outer margin ending in an articulate or nonarticulate spine; carpopropodus of thoracic endopod 6 with 3-10 (in Arthromysis up to
26) segments; two pairs of well-developed oostegites, rudimentary oostegite on thoracic
endopod 6; all pleopods of females and pleopods 1, 2 of males rudimentary; male
pleopod 3 generally biramous (uniramous in Kainommatomysis), with unsegmented
endopod and sub-segmented exopod, male pleopod 4 biramous, exopod elongate, with
modified setae, pleopod 5 rudimentary or less frequently biramous; statoliths composed
of fluorite, less frequently of vaterite; telson variable, mostly with apical cleft, this cleft
(if present) mostly armed with spine-like laminae and in several taxa also with a pair
of medio-apical plumose setae.
Type genus. – Mysis Latreille, 1802.
Seventeen genera included. – Antarctomysis Coutière, 1906 (3 species), Arthromysis
Colosi, 1924 (1), Caspiomysis G. O. Sars, 1907 (1), Hemimysis G. O. Sars, 1869
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(9), Hyperstilomysis Fukuoka, Bravo & Murano, 2005 (1), Kainommatomysis W. M.
Tattersall, 1927 (3), Katamysis G. O. Sars, 1893 (1), Mesopodopsis Czerniavsky,
1882 (8), Mysis (15), Nanomysis W. M. Tattersall, 1921 (3), Paramysis Czerniavsky,
1882 (8 subgenera, 23 species), Parastilomysis Ii, 1936 (4), Praunus Leach, 1814 (3),
†Sarmysis Maissuradze & Popescu, 1987 (3 fossil species), Schistomysis Norman, 1892
(6), Stilomysis Norman, 1892 (4), Tasmanomysis Fenton, 1985 (1).
Remarks. – Kainommatomysis is assigned here with some reservation — see
discussion in W. M. Tattersall (1927). The allocation of this genus together with the
remaining morphological heterogeneity of this tribe require further investigation.
Diamysini new tribe (figs. 54.4J, 54.12D-F, 54.18J-O, 54.21O, P, 54.35H, J, 54.44A).
Definition. – Antennal scale setose all around, generally with short apical segment
(rarely missing); carpopropodus of thoracic endopod 6 with 2-3 segments; two pairs
of well-developed oostegites, rudimentary oostegite on thoracic endopod 6; pleopods
rudimentary in both sexes, except male pleopods 3, 4; male pleopod 3 reduced to small
endopod fused with larger 2-segmented sympod, less frequently rudimentary as in
female; pleopod 4 with large, 2-segmented sympod, its exopod frequently styliform,
ending in 1 (2-3) large, modified setae; endopod of uropod with 1 (0-2) spines on
ventral face near statocyst, statoliths composed of vaterite, less frequently of fluorite;
telson shorter than ultimate pleonite, mostly with short apical cleft or at least apically
truncate, spines (if present) on lateral margins arranged in continuous series, not
arranged in groups of large spines with smaller spines in between; each lateral margin
ending in a comparatively large spine, cleft (if distinct) lined with spine-like laminae
or with small spines.
Type genus. – Diamysis Czerniavsky, 1882, by present designation.
Nine genera included. – Antromysis Creaser, 1936 (6 species), Diamysis (14),
Gangemysis Derzhavin, 1924 (1), Indomysis W. M. Tattersall, 1914 (2), Limnomysis
Czerniavsky, 1882 (1), Parvimysis Brattegard, 1969 (3), Surinamysis Bowman, 1977
(3), Taphromysis Banner, 1953 (3), Troglomysis Stammer, 1933 (1).
Anisomysini new tribe (fig. 54.19G).
Definition. – Antennal scale setose all around (exceptionally with blunt spine on
outer margin) and with short apical segment; carpopropodus of thoracic endopod 6
with 1-3 segments; two pairs of well-developed oostegites, rudimentary oostegite on
thoracic endopod 6; pleopods rudimentary in both sexes, except male pleopod 4 and
to a minor extent also pleopod 3; third male pleopod uniramous, unsegmented, mostly
rudimentary as in females or reduced to small endopod fused with sympod; exopod
of fourth male pleopod (sub)apically with 2 (1) large modified setae; uropods without
spines, statoliths composed of fluorite; telson shorter than ultimate pleonite, terminally
rounded or with apical cleft, lateral margins bare or furnished with spines; spines (if
present) on lateral margins arranged in continuous series, not arranged in groups of
large spines with smaller spines in between; telson always devoid of setae or laminae.
Type genus. – Anisomysis Hansen, 1910, by present designation.
Seven genera included. – Anisomysis (2 subgenera; 55 species), Carnegieomysis
W. M. Tattersall, 1943 (4 species), Halemysis Băcescu & Udrescu, 1984 (1), Idiomysis
W. M. Tattersall, 1922 (5), Javanisomysis Băcescu, 1992 (1), Mysidium Dana, 1852
(6), Paramesopodopsis Fenton, 1985 (1).
Neomysini new tribe.
Definition. – Antennal scale setose all around, with short apical segment; carpopropodus of thoracic endopod 6 with 4-20 segments; two pairs of well-developed
oostegites, anterior pair occasionally with a posterior lobe, sixth thoracic endopod
with additional rudimentary oostegite; pleopods rudimentary in both sexes, except male
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pleopod 4; exopod of male pleopod 4 typically large, (sub)apically with mostly 2 large
modified setae; the rudimentary pleopod 5 may be longer in males than in females;
endopod of uropods normally with closely set spines on inner margin near statocyst,
with the spines increasing in length distally (rarely without spines or spines loosely set
all along inner margin), statoliths composed of fluorite; telson prolonged, linguiform
to subtriangular, subequal to longer than ultimate pleonite, lateral margins partly or entirely armed with spines, spines in most species arranged in groups of large spines with
small spines in between.
Type genus. – Neomysis Czerniavsky, 1882, by present designation.
Twenty-one genera included. – Acanthomysis Czerniavsky, 1882 (17 species),
Alienacanthomysis Holmquist, 1981 (1), Boreoacanthomysis Fukuoka & Murano,
2004 (1), Columbiaemysis Holmquist, 1982 (1), Disacanthomysis Holmquist, 1981
(1), Exacanthomysis Holmquist, 1981 (3), Hemiacanthomysis Fukuoka & Murano,
2002 (1), Hippacanthomysis Murano & Chess, 1987 (1), Holmesimysis Holmquist,
1979 (5), Hyperacanthomysis Fukuoka & Murano, 2000 (2), Lycomysis Hansen, 1910
(2), Mesacanthomysis Nouvel, 1967 (1), Neomysis (17), Nipponomysis Takahashi &
Murano, 1986 (19), Notacanthomysis Fukuoka & Murano, 2000 (2), Orientomysis
Derzhavin, 1913 (22), Pacifacanthomysis Holmquist, 1981 (1), Paracanthomysis Ii,
1936 (4), Proneomysis W. M. Tattersall, 1933 (1), Telacanthomysis Fukuoka & Murano,
2001 (1), Xenacanthomysis Holmquist, 1980 (1).
PALAUMYSINAE Wittmann, 2013b (figs. 54.4K, 54.5K, 54.7G, 54.21U).
Definition. – Eyes well developed; inner antennular flagellum very short, reduced to
only 2-5 segments; antennal scale missing or vestigial; labrum normal; thoracopods 3-8
with the carpus separated from the propodus by a transverse articulation; two pairs of small
oostegites; penes of moderate size; all pleopods reduced to uniramous, unsegmented rods
in both sexes, pleopod 4 with modified apical spine (seta) in males only; both rami of the
uropods undivided, endopod with statocyst composed of fluorite; telson (sub)triangular,
without or with small medio-apical indentation, its lateral margins bare and each ending in
a spine.
Type genus. – Palaumysis Băcescu & Iliffe, 1986.
Two genera included. – Gironomysis Ortiz, García-Debrás & Pérez, 2000 (1 species),
Palaumysis (4).
H ETEROMYSINAE Norman, 1892 (figs. 54.1D, 54.4M, 54.5M).
Diagnosis. – Eyes well developed, rarely weakly reduced; appendix masculina varies
from well developed to very small or reduced to a brush of setae; antennal scale
setose all around; labrum, maxillula, and thoracic endopod 1 normal; digitus mobilis
present generally on both or rarely on only one mandible; thoracic endopod 3 pediform
or more frequently subchelate, prehensile; 1-3 pairs of oostegites; pleomeres without
projecting pleural plates; pleopods normally reduced to unsegmented endopods in both
sexes (pleopod 3 sub-divided in males of Harmelinella); penes tubular, in most genera
strongly developed; both rami of the uropods undivided; statocyst with fluorite statolith;
telson variable.
Inventory. – Three tribes are distinguished according to the structure of thoracic
endopod 3 and male pleopod 3. Altogether, they comprise 14 genera with a total of 124
species.
Heteromysini Norman, 1892 (figs. 54.1D, 54.4M, 54.5M, 54.18K, H, 54.20G, F, 54.21R,
S, 54.35F, G, 54.36C).
Diagnosis. – Appendix masculina very small or reduced to a brush of setae; thoracic
endopod 3 swollen, prehensile, carpopropodus two-segmented, rarely fused; thoracic
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endopods 4-8 developed as pereiopods, normal; 2-3 pairs of oostegites; penes large
(in length and/or in diameter) or rarely small, mostly tubular, mostly with distinct
terminal lobes; males of certain species with some of the pleopods bearing small
(flagellate) spines or modified setae; telson with apical cleft armed with spine-like
laminae, lateral margins smooth or distally with spines.
Type genus. – Heteromysis S. I. Smith, 1873.
Five genera included. – Heteromysis (4 subgenera; 83 species), Heteromysoides
Băcescu, 1968 (10 species), Ischiomysis Wittmann, 2013a (2), Platymysis Brattegard,
1980 (1), Retromysis Wittmann, 2004 (1).
Harmelinellini new tribe.
Definition. – Appendix masculina well developed, rounded; thoracic endopods 38 normal, endopod 3 pediform, not prehensile and not conspicuously swollen, its
carpopropodus two-segmented; penes large, tubular, stiff, not changeable in size and
form; all pleopods of the females and pleopods 1, 2, 4, 5 of males rudimentary, without
modified setae or spines; pleopod 3 of males uniramous, elongate, sub-segmented,
apically modified; telson with apical cleft armed with spine-like laminae, lateral
margins distally with spines.
Only the type genus known. – Harmelinella Ledoyer, 1989, by present designation
(1 species).
Mysidetini Holt & Tattersall, 1906 (figs. 54.20E, 54.22M).
Diagnosis. – Appendix masculina varies from well developed to very small or
reduced; thoracic endopods 3-8 normal, endopod 3 pediform, not prehensile and not
conspicuously swollen, its carpopropodus with two or more segments; 1-3 pairs of
oostegites; penes mostly long, tubular, stiff or changeable in size and form; pleopods
rudimentary and non-dimorphic, without modified setae or spines; telson entire or with
apical cleft, lateral margins distally with spines.
Discussion. – This family group taxon was defined as the subfamily Mysidetinae
by Holt & Tattersall (1906). Hansen (1910) did not accept this subfamily and retained
the genus Mysidetes in the tribe Leptomysini (Mysinae). Zimmer (1914) followed the
proposal of Hansen (1910), but with some reservation based on the reduction of the
male pleopods. Finally, W. M. Tattersall (1923) himself withdrew the Mysidetinae.
However, this does not diminish the nomenclatorial availability of the taxon (see Article
11 in ICZN, 1999). Here, the taxon is revived at tribus level due to the structure of
thoracic endopod 3, penes, male pleopods, and telson.
Type genus. – Mysidetes Holt & Tattersall, 1906.
Eight genera included. – Bermudamysis Băcescu & Iliffe, 1986 (1 species), Burrimysis Jaume & Garcia, 1993 (1), Deltamysis Bowman & Orsi, 1992 (1), Kochimysis
Panampunnayil & Biju, 2007 (1), Mysidetes (16), Mysifaun Wittmann, 1996 (1), Platyops Băcescu & Iliffe, 1986 (1), Pseudomysidetes W. M. Tattersall, 1936 (4).
M YSIDELLINAE Czerniavsky, 1882 (figs. 54.4L, 54.5L, 54.21T).
Diagnosis. – Antennal scale setose all around; labrum with strongly asymmetrical
posterior lobes; mandibles with large cutting edge without teeth; maxillula with inwards
bent lobes; thoracic endopod 1 with strongly expanded propodus; thoracic endopod
3 normal, not prehensile; three pairs of oostegites; penes tubular, strongly developed;
pleomeres without projecting pleural plates; pleopods rudimentary in both sexes; uropods
without spines, both rami of the uropods undivided; statocyst with fluorite statolith; telson
with apical cleft.
Only the type genus known. – Mysidella G. O. Sars, 1872 (16 species).
342
Keys to the families, subfamilies, and tribes of the Lophogastrida,
Stygiomysida, and Mysida
Note. – Habitus figures are given in figs. 54.1-54.5 as examples for all extant taxa at
order, family, and subfamily level.
Eumalacostraca with caridoid habitus; eyes generally stalked; carapace well developed, forming
ventrally open, lateral chambers, with its posterior portions freely projecting over some of the
ultimate thoracomeres in most taxa; eight pairs of generally biramous thoracopods; oostegites present
on (mostly the ultimate) 1-7 pairs of thoracopods; gonopores on the sixth thoracomere in females,
and on the coxae of the eighth thoracopods in males; well-developed pleon, capable of tail flipping;
strong tail fan formed by the telson and a pair of biramous uropods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1a. Branchiae emerge from 5-7 pairs of thoracopods; females with (so far known) seven pairs
of oostegites; pleopods well developed, biramous in both sexes; uropods without statocyst
(†Pygocephalomorpha, Lophogastrida) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1b. No branchiae present; instead, the inner wall of the lateral carapace chambers is lined with
respiratory tissue; female pleopods reduced to some extent in most taxa; 1-7 pairs of oostegites;
uropods with or without statocyst (Stygiomysida, Mysida) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2a. Carapace broad, with branchiostegal development of the pleura in order to accommodate the
branchiae; no tubular penes known; telson with well-developed, lobe- or spine-like apical and
furcal processes . . . . . . . . Order †Pygocephalomorpha Beurlen, 1930. Carboniferous-Permian.
2b. Ramified branchiae entirely or only partly covered by the carapace in lateral view; male
gonopores on the coxa of each thoracopod 8 in extant forms, the orifices are not elevated or are
on top of a small elevation, no lobes around orifice and no tubular penes present; pleopods not
modified or only weakly modified in males
Order Lophogastrida Boas, 1883. Carboniferous-Recent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3a. Pleomeres without projecting pleural plates, ultimate pleomere not divided by a transversal
furrow; thoracic endopods 1-4 developed as maxillipeds (gnathopods)
. . . . . . . . . . . . . . . . . . . . . . . Eucopiidae G. O. Sars, 1885 (figs. 54.2D, 54.19A). Triassic-Recent.
3b. Pleomeres with well-developed pleural plates; at least thoracic endopods 3-7 are pediform
....................................................................................4
4a. All thoracic endopods pediform, not specialized as maxillipeds; ultimate pleomere (as far as
known) not divided by a transversal furrow
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . †Peachocarididae Schram, 1986. Carboniferous.
4b. At least thoracic endopod 1 developed as maxilliped; ultimate pleomere more or less distinctly
divided by a transversal furrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5a. Only thoracic endopod 1 developed as maxilliped
. . . . . . . . . . . . . . . . . . . . . . . . . . . . Gnathophausiidae Udrescu, 1984 (figs. 54.1A, 54.2A). Recent.
5b. Thoracic endopods 1, 2 developed as maxillipeds
. . . . . . . . . . . . . . . . . . . . . . . . . . Lophogastridae G. O. Sars, 1870 (fig. 54.2B, C). Jurassic-Recent.
6a. Eyes normal or less frequently reduced; well-developed tubular penes (except in Rhopalophthalminae); pleopods 2-5 (mostly also 1) reduced to unsegmented plates or rods in females (but
well developed, biramous in Archaeomysini), partly also reduced in males; sympod of uropods
without inner lobe, endopod with or without statocyst (Mysida) . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6b. Cornea reduced to varying extent; gonopores flanked by two lobes, no tubular penes developed;
all pleopods biramous but rudimentary in both sexes, sympod and endopod unsegmented, but
exopod with a small number of segments; sympod of uropod with spinose inner lobe, statocysts
absent
Order Stygiomysida Tchindonova, 1981. Recent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7a.
7b.
8.
9a.
9b.
10a.
10b.
11.
12a.
12b.
13a.
13b.
14a.
14b.
15a.
15b.
343
Antennal scale vestigial; carapace short, completely fused with the anterior thoracomeres,
giving the body a vermiform shape; maxillula without palp; thoracic endopods 1-4 modified as
maxillipeds, endopods 5-8 pediform, females with oostegites on thoracopods 4-7 only; sympod
of uropod with large inner lobe whose apical spines extend beyond the endopod
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stygiomysidae Caroli, 1937 (figs. 54.1B, 54.3A).
Antennal scale well developed; carapace large, projecting freely over several posterior thoracomeres and giving the body a shrimp-like appearance; maxillula with palp; thoracic endopods
1-3 modified as maxillipeds, endopods 4-8 pediform, females with oostegites on thoracopods
2-8; sympod of uropod with small, spinose inner lobe
. . . . . . . . . . . . . . . . . . . . . . . . . . . Lepidomysidae Clarke, 1961 (figs. 54.1C, 54.3B-D, 54.19C, D).
Carapace projects freely over several posterior thoracomeres (except in Palaumysis philippinensis); 1-2 pairs of pleopods with particular modifications in males of most taxa
Order Mysida Boas, 1883. Jurassic-Recent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Endopods of uropods always with statocyst; merus of thoracic endopod 2 without large lobelike expansion; all thoracopods normally with natatory exopod; maxillula mostly with palp;
females with 1-7 pairs of oostegites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Endopods of uropods without statocyst; merus of thoracic endopod 2 with a large lobe-like
expansion; thoracopod 1, often also thoracopod 2, without natatory exopod; maxillula without
palp; females with 7 pairs of oostegites
Petalophthalmidae Czerniavsky, 1882. Recent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Mandibular palp strongly enlarged, prehensile; only first thoracopod without natatory exopod
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Petalophthalminae Czerniavsky, 1882 (figs. 54.4A, 54.12B).
Mandibular palp normal, not prehensile; first as well as second thoracopod without natatory
exopod . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hansenomysinae, new subfamily (figs. 54.5A, 54.12A).
Well-developed tubular penes except in Rhopalophthalmus; endopods of uropods normally
undivided (subdivided in Rhopalophthalmus)
Mysidae Haworth, 1825. Jurassic-Recent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Seven pairs of oostegites; exopod of uropods divided by a proximal, incomplete suture,
endopod not subdivided; smooth outer margin of the antennal scale ending in a non-articulate
spine; male pleopods biramous throughout; telson with apical cleft
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Boreomysinae Holt & Tattersall, 1905 (figs. 54.4B, 54.5B).
Females with less than 5, mostly 2-3, pairs of oostegites; exopod of uropods not subdivided or
with a subterminal, but never a proximal suture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Both rami of the uropods not subdivided (7 subfamilies) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Exopod of uropods divided by a subapical suture; telson elongate, linguiform; antennal scale
well developed, with smooth outer margin ending in a non-articulate spine (Rhopalophthalminae, Siriellinae) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Both rami of the uropods divided by a suture at about 25-30% length from tip; thoracic endopod
8 small or minute; no tubular penes developed; exopod of uropods without spines, setose all
around; male pleopods biramous, exites of endopods not strongly curved or coiled
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rhopalophthalminae Hansen, 1910 (figs. 54.4C, 54.5C).
Endopods of uropods not subdivided; thoracic endopods 3-8 well developed, with peculiar
brush of setae around dactylus; penes well developed; exopod of uropods with spines on outer
margin of the basal segment
Siriellinae Czerniavsky, 1882 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Male pleopods 1-5 biramous, multi-segmented except in endopod 1, basal segment of endopods
with spirally coiled or curved, less frequently straight exites (= pseudobranchial lobes)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Siriellini Czerniavsky, 1882 (figs. 54.4D, 54.5D, 54.26A).
Male pleopods 1-3, 5 rudimentary, uniramous and unsegmented as in females; male pleopod 4
with two multi-segmented rami, basal segment of endopod with straight, rod-like exite
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metasiriellini Murano, 1986.
344
16a. First pleomere without projecting pleural plates in both sexes; exopod of male pleopod 3 not
conspicuously elongate, terminally not or only weakly modified (6 subfamilies) . . . . . . . . . . . 19
16b. First pleomere of female with pleural plates supporting the marsupium; male pleopod 3 with
elongate, strongly modified exopod; antennal scale with smooth outer margin ending in a nonarticulate spine; telson with spines on lateral margins, its apical cleft armed with spine-like
laminae
Gastrosaccinae Norman, 1892 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
17a. First pleomere with small pleural plates covering a small part of the marsupium, no such
plates in males; female pleopods uniramous, unsegmented; male pleopod 1, in part also 4,
5, rudimentary, resembling those in females, remaining male pleopods biramous, exopod 3
modified in diverse, in part complex ways
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anchialinini, new replacement name (figs. 54.4E, 54.5E).
17b. First pleomere with large pleural plates covering and supporting the marsupium from behind,
in part also from the side; female pleopod 1 biramous (Archaeomysini, Gastrosaccini) . . . . . 18
18a. First pleomere without pleural plates in males; female pleopods 2-5 uniramous, unsegmented;
male pleopods biramous or reduced in various ways, exopod 3 (exceptionally exopod 4)
particularly long and modified in diverse, in part complex ways
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gastrosaccini Norman, 1892 (figs. 54.4F, 54.5F).
18b. First pleomere with pleural plates also present in males, but smaller than in females; certain
taxa with plates on additional pleomeres, whereby plate size decreases from pleura 2 to 5;
pleopods biramous in both sexes, exopod of pleopod 3 elongated in males only
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Archaeomysini Czerniavsky, 1882.
19a. All pleopods uniramous, representing endopods in both sexes; endopods 4, 5 not elongate in
males (Heteromysinae, Mysidellinae, Palaumysinae) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
19b. All pleopods uniramous in both sexes; endopods of male pleopods 4, 5 elongate (Erythropinae:
Calyptommini) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
19c. All male pleopods or at least male pleopod 4 biramous, all female pleopods uniramous
(Mysinae, Leptomysinae, Erythropinae in part) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
20a. Exopod of male pleopod 4 not conspicuously elongate, mostly without modified setae; oblique
or less frequently transverse articulation between carpus and propodus of thoracic endopods
3-8 (Erythropinae in part) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
20b. Exopod of male pleopod 4 elongate, with modified setae (never on endopod); always with
transverse articulation between carpus and propodus of thoracic endopods 3-8 (Mysinae,
Leptomysinae) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
21a. Male pleopods 1, 2 always uniramous, rudimentary as in females; male pleopod 4 and in certain
taxa also pleopod 3, exceptionally also pleopod 5, biramous; antennal scale variable; females
with two pairs of well-developed oostegites, rarely with three
Mysinae Haworth, 1825 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
21b. Male pleopods 2-5 always biramous, mostly multi-segmented; antennal scale setose all around;
females with three pairs of well-developed oostegites, rarely with only two
Leptomysinae Czerniavsky, 1882 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
22a. Exopod of maxilla narrow; first thoracic endopod (5-6)-segmented, its ischium fused with the
merus; telson mostly entire, or with small apical indentation, its margins with spines but without
setae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mysidopsini, new tribe (figs. 54.15L, 54.18F, 54.22N).
22b. Exopod of maxilla laterally well expanded; first thoracic endopod seven-segmented, its ischium
and merus not fused; telson variable (Leptomysini, Afromysini) . . . . . . . . . . . . . . . . . . . . . . . . . 23
23a. Telson entire or with minute cleft, its margins with spines but without laminae or apical setae;
distal segment of endopod of maxilla not conspicuously widened
. . . . . . . . . . . . . . . . . . . Leptomysini Czerniavsky, 1882 (figs. 54.4H, 54.5H, 54.21N, 54.36E-F).
345
23b. Telson apically with distinct cleft or less frequently narrowly truncate; apical cleft, if present,
mostly with two plumose setae emerging from or close to its bottom, margins of cleft smooth
or lined by spine-like laminae; distal segment of endopod of maxilla often terminally widened
and with spines or teeth on terminal margin . . . . . . . . . . . . . Afromysini, new tribe (fig. 54.25F).
24a. Male pleopod 3 uniramous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
24b. Male pleopod 3 biramous
. . . . . . . . . . . Mysini (without genus Kainommatomysis) (figs. 54.1E, 54.4J, 54.5J, 54.36A, B).
25a. Cornea bipartite, posterior part with large, backward-oriented ommatidium bearing a conical
lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mysini (genus Kainommatomysis).
25b. Cornea normal, not bipartite (Diamysini, Anisomysini, Neomysini) . . . . . . . . . . . . . . . . . . . . . . 26
26a. Carpopropodus of thoracic endopod 6 with 4-20 segments; telson entire, linguiform to elongate
subtriangular, its lateral margins with spines organized in groups of large spines with smaller
ones in between, less frequently in nearly continuous series; male pleopod 3 reduced to small
plate as in females . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neomysini, new tribe (fig. 54.19G).
26b. Carpopropodus of thoracic endopod 6 with only 1-3 segments; telson shorter, with variable
shape, its lateral margins bare or with spines arranged in a nearly continuous series of size, i.e.,
not arranged in groups of different size (Diamysini, Anisomysini) . . . . . . . . . . . . . . . . . . . . . . . 27
27a. Male pleopod 3 reduced to small endopod fused with larger 2-segmented sympod, less
frequently rudimentary as in female; endopod of uropod with mostly one (0-2) spine on ventral
face near statocyst; telson mostly with short apical cleft or at least apically truncate; lateral
margins ending in a distinctly larger spine compared to the remaining ones, cleft (if distinct)
lined with spine-like laminae or with small spines
. . . . . . . . . . . . . . . . . . . . . Diamysini, new tribe (figs. 54.4J, 54.18J, M, O, 54.21O, P, 54.35H, J).
27b. Male pleopod 3 normally rudimentary as in females, rarely reduced to small endopod fused
with sympod; uropods without spines; telson terminally rounded or with apical cleft, lateral
margins bare or furnished with spines of mostly subequal size; telson always devoid of laminae
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anisomysini, new tribe.
28. Antennal scale with its outer margin ending in a spine, less frequently setose all around or
vestigial; telson entire or rarely terminally indented or cleft
Erythropinae Hansen, 1910 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
29a. Eyestalks separate; antennal gland normal or hypertrophic (5 tribes) . . . . . . . . . . . . . . . . . . . . . 31
29b. Eyestalks fused to a common plate or connected by a median bridge; antennal gland hypertrophic (Calyptommini, Pseudommini, Mysimenziesini) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
30a. Both eyes fused to a transverse lamina without cleft, visual elements rudimentary or absent;
basal segment of antennular peduncle normal; lateral margins of telson not serrate but smooth,
terminally with spines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calyptommini W. M. Tattersall, 1909.
30b. Both eyes fused to a common plate with anterior, median cleft, visual elements missing; basal
segment of antennular peduncle normal; lateral margins of telson not serrate but smooth,
terminally with or without spines. . . . .Pseudommini, new tribe (figs. 54.20C, 54.21J, 54.25P).
30c. Rudimentary, horn-like eyestalks connected by a median bridge; basal segment of antennular
peduncle medio-dorsally with sensory fossette or with setose elevation; lateral margins of
telson distinctly serrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mysimenziesini Tchindonova, 1981.
31a. Antennal scale absent or vestigial; eyes well developed; labrum normal; 2 pairs of oostegites;
thoracic endopods 3-8 with the carpus separated from the propodus by a transverse or a slightly
oblique articulation . . . . . . . . . . . . Arachnomysini Holt & Tattersall, 1905 (figs. 54.7F, 54.12C).
31b. Antennal scale well developed; eyes normal or reduced to varying extent . . . . . . . . . . . . . . . . . 32
32a. Eyestalks reduced to a pair of immotile plates, cornea rudimentary or absent; thoracic endopods
3-8 with transverse articulation between carpus and propodus; labrum normal
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amblyopsini Tchindonova, 1981 (figs. 54.4G, 54.18D).
32b. Eyes mostly normal or reduced to varying degrees, not plate-like . . . . . . . . . . . . . . . . . . . . . . . . 33
346
33a. Labrum strongly asymmetrical; four pairs of oostegites; endopods 3-8 with carpus separated
from propodus by transverse articulation . . . . . . . . . . . . . . . . . . . Thalassomysini Nouvel, 1942b.
33b. Labrum normal; 2-3 pairs of well-formed oostegites; thoracic endopods 3-8 with oblique or
less frequently with transverse articulation between carpus and propodus . . . . . . . . . . . . . . . . . 34
34a. All pleopods uniramous in both sexes; male pleopod 4 represented as elongate, multisegmented endopod; remaining pleopods unsegmented, rudimentary
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inusitatomysini, new tribe.
34b. All pleopods biramous in males, whereas uniramous, rudimentary in females
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Erythropini Hansen, 1910 (fig. 54.5G).
35a. Antennal scale missing or vestigial; inner antennular flagellum very short, reduced to only 2-5
segments; penes of moderate size; labrum normal; telson (sub)triangular, without or with small
medio-apical indentation
. . . . . . . . . . . . . . . . . . . . . . Palaumysinae Wittmann, 2013b (figs. 54.4K, 54.5K, 54.7G, 54.21U).
35b. Antennal scale well developed, setose all around; inner antennular flagellum long, multisegmented as usual; penes strongly developed in most taxa, rarely small (Mysidellinae,
Heteromysinae) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
36a. Labrum with asymmetrical posterior lobes; mandibles with large cutting edge without teeth;
maxillula with inwards bent lobes; thoracic endopod 1 with strongly expanded propodus;
thoracic endopod 3 normal, not prehensile; telson with apical cleft
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mysidellinae Czerniavsky, 1882 (figs. 54.4L, 54.5L, 54.21T).
36b. Labrum, mandibles, maxillula, and thoracic endopod 1 normal; thoracic endopod 3 normal or
prehensile; structure of telson varies between tribes
Heteromysinae Norman, 1892 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
37a. Thoracic endopod 3 developed as gnathopod, swollen, prehensile, its carpopropodus twosegmented, rarely fused; males of certain taxa with some of the pleopods bearing small
(flagellate) spines or modified setae; telson with apical cleft
. . . . . . . . . . . Heteromysini Norman, 1892 (figs. 54.1D, 54.4M, 54.5M, 54.18K, H, 54.21R, S).
37b. Thoracic endopod 3 pediform, not prehensile and not conspicuously swollen, its carpopropodus
with two or more segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
38a. Carpopropodus of thoracic endopod 3 with two or more segments; all pleopods reduced to
unsegmented plates, without modified setae or spines in both sexes; telson entire or with apical
cleft . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mysidetini Holt & Tattersall, 1906 (figs. 54.20E, 54.22M).
38b. Carpopropodus of thoracic endopod 3 with two segments; most pleopods of males rudimentary
as in females, without modified setae or spines; by contrast, male pleopod 3 elongate, subsegmented, apically modified; telson with apical cleft . . . . . . . . . . . . . Harmelinellini, new tribe.
ACKNOWLEDGEMENTS
The authors are greatly indebted to Jean-Paul Casanova (France) for consent to
translate and integrate his contributions to the treatise of Nouvel et al. (1999) into the
present work. Consent to reproduce previously published figures was generously given
(besides institutional copyright holders) by the authors Lisandro de Almeida (Brazil), JeanPaul Casanova (figures other than from 1999), Mikhail Daneliya (Helsinki), Laetitia De
Jong-Moreau (Marseille), Marc Espeel (Ghent), Yukio Hanamura (Yokohama), Salvatore
Inguscio (Nardò), Kenneth Meland (Bergen), Masaaki Murano (Tokyo), Victor Petryashov
(St. Petersburg), César Vilas-Fernández (Cádiz), Christian Wirkner (Rostock), and Peter
Wirtz (Funchal). Originals of published drawings (fig. 54.31A, C) were kindly provided
347
by C. Wirkner. Original photos were generously supplied by L. de Almeida, José Antonio
González (Las Palmas), S. Inguscio, and P. Wirtz. Sincere thanks to the editors J. C. von
Vaupel Klein (Bilthoven) and Frederick R. Schram (Langley, WA) for their invitation
to write this chapter, for proposing improvements, and for their great patience with our
repeated emendations.
A PPENDIX
Taxa at species and genus level in the text and figures of this chapter are listed with authorities and
dates of their description. Data on synonymy or homonymy are indicated wherever necessary. For
names of genera not given below see above, ‘Classification’
Acanthomysis aspera Ii, 1964
Acanthomysis longicornis (H. Milne Edwards, 1837)
Acanthomysis robusta Murano, 1984
Acanthomysis sculpta (W. M. Tattersall, 1933)
Acanthomysis thailandica Murano, 1986
Aiptasia mutabilis (Gravenhorst, 1831)
Amblyopsoides crozetii (Willemoës-Suhm in G. O. Sars, 1884)
Amblyopsoides ohlinii (W. M. Tattersall, 1951)
Americamysis almyra (Bowman, 1964)
Americamysis bahia (Molenock, 1969)
Americamysis bigelowi (W. M. Tattersall, 1926)
Amphilina foliacea (Rudolphi, 1819)
Anchialina agilis (G. O. Sars, 1877)
Anchialina truncata (G. O. Sars, 1883)
Anchialina typica (Krøyer, 1861)
Anchialus Krøyer, 1861, junior homonym of the coleopteran genera Anchialus Gistel, 1834, and
Anchialus Thomson, 1859; replaced by the valid Anchialina Norman & Scott, 1906
Anemonia viridis (Pennant, 1777)
Anisakis simplex (Rudolphi, 1809)
Anisomysis levi Băcescu, 1973
Antarctomysis maxima Holt & Tattersall, 1906
Antarctomysis ohlinii Hansen, 1908
Antromysis cubanica Băcescu & Orghidan, 1971
Antromysis juberthiei Băcescu & Orghidan, 1977
Archaeomysis articulata Hanamura, 1997
Archaeomysis grebnitzkii Czerniavsky, 1882
Archaeomysis vulgaris (Nakazawa, 1910)
Artemia Leach, 1819
Bacescomysis abyssalis (Lagardère, 1983)
Bartholomea annulata (Lesueur, 1817)
Birsteiniamysis inermis (Willemoës-Suhm, 1874)
Boreomysis arctica (Krøyer, 1861)
Boreomysis californica Ortmann, 1894
Boreomysis megalops G. O. Sars, 1872
Boreomysis microps G. O. Sars, 1883
Boreomysis obtusata G. O. Sars, 1884
Boreomysis scyphops G. O. Sars, 1879, junior synonym of Birsteiniamysis inermis
Branchiomma nigromaculatum (Baird, 1865)
Bunocotyle cingulata Odhner, 1928
348
Caesaromysis hispida Ortmann, 1893
Cancer Linnaeus, 1758
Cancer bipes Fabricius, 1780, outdated original combination of Nebalia bipes
Cancer flexuosus O. F. Müller, 1776, outdated original combination of Praunus flexuosus
Cancer oculatus Fabricius, 1780, outdated original combination of Mysis oculata
Cancer pedatus Fabricius, 1780, suppressed name (ICZN, 1959) (euphausiid?)
Cassiopea Péron & Lesueur, 1810
Ceratolepis hamata G. O. Sars, 1883
Ceratomysis spinosa Faxon, 1893
Cercopagis pengoi (Ostroumov, 1891)
Chalaraspidum alatum (Willemoës-Suhm, 1876)
Chlamydopleon aculeatum Ortmann, 1893
Chunomysis diadema Holt & Tattersall, 1905
Coifmanniella johnsoni (W. M. Tattersall, 1937)
Cymodocea K. D. König, 1806
Dactylerythrops dactylops Holt & Tattersall, 1905
Daphnia O. F. Müller, 1785
Dardanus Paulson, 1875
Diadema Gray, 1825
Diadema antillarum Philippi, 1845
Diamysis bacescui Wittmann & Ariani, 1998
Diamysis bahirensis (G. O. Sars, 1877)
Diamysis camassai Ariani & Wittmann, 2002
Diamysis cymodoceae Wittmann & Ariani, 2012
Diamysis fluviatilis Wittmann & Ariani, 2012
Diamysis lagunaris Ariani & Wittmann, 2000
Diamysis mesohalobia Ariani & Wittmann, 2000
Dioptromysis paucispinosa Brattegard, 1969
Dioptromysis perspicillata Zimmer, 1915
Dollocaris ingens van Straelen, 1923
Echinorhynchus leidyi Van Cleve, 1924
Elder unguiculata Münster, 1839
Erythrops abyssorum (G. O. Sars, 1869)
Erythrops serratus (G. O. Sars, 1863)
Euchaetomera zurstrasseni (Illig, 1906)
Eucopia australis Dana, 1852
Eucopia crassicornis Casanova, 1997
Eucopia grimaldii H. Nouvel, 1942
Eucopia major Hansen, 1910
Eucopia precursor Secretan & Riou, 1986
Eucopia sculpticauda Faxon, 1893
Eucopia unguiculata (Willemoës-Suhm, 1875)
Francocaris grimmi Broili, 1917
Gastrosaccus brevifissura O. S. Tattersall, 1952
Gastrosaccus psammodytes O. S. Tattersall, 1958
Gastrosaccus roscoffensis Băcescu, 1970
Gastrosaccus sanctus (Van Beneden, 1861)
Gastrosaccus spinifer (Goës, 1864)
349
Gastrosaccus widhalmi (Czerniavsky, 1882)
Gastrosaccus yuyu Bamber & Morton, 2012
Gnathophausia affinis G. O. Sars, 1884
Gnathophausia childressi Casanova, 1996
Gnathophausia gigas Willemoës-Suhm, 1873
Gnathophausia ingens (Dohrn, 1870)
Gnathophausia longispina G. O. Sars, 1883
Gnathophausia zoea Willemoës-Suhm, 1873
Haemulon flavolineatum (Desmarest, 1823)
Hansenomysis atlantica Lagardère, 1983
Hansenomysis abyssalis Lagardère, 1983
Hansenomysis falklandica O. S. Tattersall, 1955
Hansenomysis nouveli Lagardère, 1983
Hansenomysis pseudofyllae Lagardère, 1983
Haplostylus lobatus (H. Nouvel, 1951)
Haplostylus magnilobatus (Băcescu & Schiecke, 1974)
Hemimysis anomala G. O. Sars, 1907
Hemimysis lamornae (Couch, 1856)
Hemimysis lamornae mediterranea Băcescu, 1937
Hemimysis margalefi Alcaraz, Riera & Gili, 1986
Hemimysis speluncola Ledoyer, 1963
Heteromysis actiniae Clarke, 1955
Heteromysis arianii Wittmann, 2000
Heteromysis armoricana H. Nouvel, 1940
Heteromysis dardani Wittmann, 2008
Heteromysis harpax (Hilgendorf, 1879)
Heteromysis harpaxoides Băcescu & Bruce, 1980
Heteromysis wirtzi Wittmann, 2008
Heteromysoides cotti (Calman, 1932)
Idiomysis inermis W. M. Tattersall, 1922
Idiomysis tsurnamali Băcescu, 1973
Idotea balthica (Pallas, 1772)
Ischiomysis peterwirtzi Wittmann, 2013
Ischiomysis telmatactiphila Wittmann, 2013
Kainommatomysis foxi W. M. Tattersall, 1927
Kainommatomysis schieckei Băcescu, 1973
Kilianicaris lerichei van Straelen, 1923
Lepidomysis Clarke, 1961, junior synonym of Spelaeomysis Caroli, 1924
Lepidophthalmus servatus Fage, 1924, invalid original combination for Spelaeomysis servata; genus
name is a junior homonym of the decapod genus Lepidophthalmus Holmes, 1904
Lepidops Zimmer, 1927, invalid replacement name for Lepidophthalmus Fage, 1924, in turn a junior
synonym of Spelaeomysis Caroli, 1924; junior homonym of the decapod genus Lepidops Miers,
1878
Leptomysis buergii Băcescu, 1966
Leptomysis gracilis (G. O. Sars, 1864)
Leptomysis heterophila Wittmann, 1986
Leptomysis lingvura (G. O. Sars, 1868)
Leptomysis lingvura marioni Gourret, 1888
350
Leptomysis mediterranea G. O. Sars, 1877
Leptomysis posidoniae Wittmann, 1986
Leptomysis truncata sardica G. O. Sars, 1877
Limnomysis benedeni Czerniavsky, 1882
Longithorax fuscus Hansen, 1908
Lophogaster affinis Colosi, 1930
Lophogaster erythraeus Colosi, 1930
Lophogaster longirostris Faxon, 1896
Lophogaster pacificus Băcescu, 1985
Lophogaster schmidti Fage, 1940
Lophogaster spinosus Ortmann, 1907
Lophogaster subglaber Hansen, 1927
Lophogaster typicus M. Sars, 1857
Lophogaster voultensis Secretan & Riou, 1986
Megalophthalmus Fabricianus Leach, 1830, suppressed name (ICZN, 1959) (an euphausiid?)
Mesopodopsis aegyptia Wittmann, 1992
Mesopodopsis africana O. S. Tattersall, 1952
Mesopodopsis orientalis (W. M. Tattersall, 1908)
Mesopodopsis slabberi (Van Beneden, 1861)
Mesopodopsis tenuipes Hanamura et al., 2008
Mesopodopsis wooldridgei Wittmann, 1992
Metamysidopsis elongata (Holmes, 1900)
Metamysidopsis neritica Bond-Buckup & Tavares, 1992
Mysidella biscayensis Lagardère & Nouvel, 1980
Mysidella typhlops G. O. Sars, 1872
Mysidella typica G. O. Sars, 1872
Mysidetes intermedia O. S. Tattersall, 1955
Mysidetes posthon Holt & Tattersall, 1906
Mysidium columbiae (Zimmer, 1915)
Mysidium gracile (Dana, 1852)
Mysidium integrum W. M. Tattersall, 1951
Mysidobdella borealis (Johansson, 1898)
Mysidopsis californica W. M. Tattersall, 1932
Mysidopsis gibbosa G. O. Sars, 1864
Mysidopsis oligocenica De Angeli & Rossi, 2006 [originally described as Mysidopsis oligocenicus;
disagreement in gender with the generic name corrected here]
Mysidopsis robustispina Brattegard, 1969
Mysifaun erigens Wittmann, 1996
Mysis diluviana Audzijonyte & Väinölä, 2005
Mysis Fabricii Leach, 1815, junior synonym of Mysis oculata
Mysis mixta Lilljeborg, 1852
Mysis oculata (Fabricius, 1780)
Mysis relicta Lovén, 1862
Mysis salemaai Audzijonyte & Väinölä, 2005
Mysis stenolepis S. I. Smith, 1873
Nebalia bipes (Fabricius, 1780)
Nebaliopsis typica G. O. Sars, 1887
Neomysis americana (S. I. Smith, 1873)
Neomysis awatschensis (Brandt, 1851)
351
Neomysis integer (Leach, 1814)
Neomysis intermedia (Czerniavsky, 1882)
Neomysis japonica Nakazawa, 1910
Neomysis mercedis Holmes, 1896
Neomysis rayii (Murdoch, 1885)
Orientomysis mitsukurii (Nakazawa, 1910)
Palaumysis philippinensis Hanamura & Kase, 2002
Palaumysis pilifera Hanamura & Kase, 2003
Palaumysis simonae Băcescu & Iliffe, 1986
Paraleptomysis dimorpha Wittmann, 1986
Paralichthys olivaceus Temminck & Schlegel, 1846
Paralophogaster glaber Hansen, 1910
Paralophogaster foresti Băcescu, 1981
Paramesopodopsis rufa Fenton, 1985
Paramysis arenosa (G. O. Sars, 1877)
Paramysis bakuensis G. O. Sars, 1895
Paramysis helleri (G. O. Sars, 1877)
Paramysis inflata (G. O. Sars, 1907)
Paramysis lacustris (Czerniavsky, 1882)
Paramysis nouveli Labat, 1953
Paramysis pontica Băcescu, 1940
Paramysis portzicensis H. Nouvel, 1950
Paramysis ullskyi Czerniavsky, 1882
Paranchialina angusta (G. O. Sars, 1883)
Parapseudomma calloplura (Holt & Tattersall, 1905)
Peachocaris acanthouraea Schram, 1984
Peachocaris strongi (Brooks, 1962)
Petalophthalmus armiger Willemoës-Suhm, 1875
Posidonia K. D. König, 1805
Praunus flexuosus (O. F. Müller, 1776)
Praunus inermis (Rathke, 1843)
Praunus neglectus (G. O. Sars, 1869)
Pseudomma affine G. O. Sars, 1870
Pseudomma armatum Hansen, 1913
Pseudomma oculospinum W. M. Tattersall, 1951
Pyroleptomysis rubra Wittmann, 1985
Rhopalophthalmus egregius Hansen, 1910
Rhopalophthalmus longicauda O. S. Tattersall, 1957
Rhopalophthalmus tartessicus Vilas-Fernández, Drake & Sorbe, 2008
Rhopalophthalmus tattersallae Pillai, 1961
Rhopalophthalmus terranatalis O. S. Tattersall, 1957
Schimperella acanthocercus Taylor, Schram & Yan-Bin, 2001
Schimperella beneckei Bill, 1914
Schimperella kessleri Bill, 1914
Schistomysis assimilis (G. O. Sars, 1877)
Schistomysis kervillei (G. O. Sars, 1885)
Schistomysis ornata (G. O. Sars, 1864)
Schistomysis spiritus (Norman, 1860)
352
Sinelobus stanfordi (Richardson, 1901)
Siriella adriatica Hoenigman, 1960, junior synonym of Siriella gracilipes
Siriella antiqua Secretan & Riou, 1986
Siriella armata (H. Milne Edwards, 1837)
Siriella carinata Secretan & Riou, 1986
Siriella castellabatensis Ariani & Spagnuolo, 1976
Siriella clausii G. O. Sars, 1877
Siriella gracilipes H. Nouvel, 1942
Siriella gracilis Dana, 1852
Siriella thompsonii (H. Milne Edwards, 1837)
Spelaeomysis bottazzii Caroli, 1924
Spelaeomysis cardisomae Bowman, 1973
Spelaeomysis cochinensis Panampunnayil & Viswakumar, 1991
Spelaeomysis longipes (Pillai & Mariamma, 1964)
Spelaeomysis nuniezi Băcescu & Orghidan, 1971
Spelaeomysis olivae Bowman, 1973
Spelaeomysis quinterensis (Villalobos, 1951)
Spelaeomysis servata (Fage, 1924) [Caroli (1924) clearly indicated female gender upon first
description of the genus by spelling “la Spelaeomysis”, where in Italian “la” is the female,
singular, definite article. Clarke (1961a) used the correct ending of the species name by
recombining Lepidophthalmus servatus Fage, 1924, to the binomen Lepidomysis servata (Fage,
1924). Ingle (1972) did not acknowledge the genus Lepidomysis Clarke, 1961a, and proposed the
new combination Spelaeomysis servatus (Fage, 1924), however, without taking account to the
previously defined gender of Spelaeomysis. Disagreement in gender of species name is corrected
by present authors (Article 34.2 of ICZN, 1999)]
Stygiomysis aemete Wagner, 1992
Stygiomysis cokei Kallmeyer & Carpenter, 1996
Stygiomysis holthuisi (Gordon, 1958)
Stygiomysis hydruntina Caroli, 1937
Stygiomysis ibarrae Ortiz, Lalana & Perez, 1996
Stygiomysis major Bowman, 1976
Surinamysis merista (Bowman, 1980)
Telmatactis cricoides (Duchassaing, 1850)
Tenagomysis tasmaniae Fenton, 1991
Thalassia Banks ex K. D. König, 1805
Troglomysis vjetrenicensis Stammer, 1933
Zoothamnium duplicatum Kahl, 1933
Zostera Linnaeus, 1753
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Gesellschaft Naturforschender Freunde zu Berlin, 18: 326-347.

the crustacea

Transcription

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